I believe what you need more than prayer, if I may, is for you to deliberately and willfully obey one of the Ten Commandments: Honor your father and your mother.
Couple months ago I asked this one question after listening to a sermon - what is the most honoring thing I can do for God? I went through my list and concluded that obeying the Ten Commandments is what I can do to honor God the most at the time. I went through the commandments and decided to focus on the 5th one - You shall honor your father and your mother. I thought I was pretty good with this command since I consider myself as a good son and have a pretty close relationship with them, especially with my mom. However, I noticed that there was something in me that requires my attention when I took a close look at all the interaction with my parents, ones including arguments and just life interaction. Whenever I get into an argument with either one of them it is usually because about their relationship. They are still married but not in good terms and I wouldn't be surprised if they file for a divorce any day. Anyways, I began to honor them as much as possible within my ability as a Christian. You know Noel, honoring someone means you defer to them. For instance, if your mom is telling people about where she went and what she saw yesterday and she is not accurate in her story, you don't correct her by saying, "Mom, it was red t-shirt, not blue," or "Mom, there were three puppies, not five." You get the idea, right? If you were with this love of your life (or let's say your favorite female celebrity if there's one) and she's telling people the story about how you and her went to this place and did what and in her story she makes a mistake, would you correct her in front of everyone? You defer to her and just let her finish her story. Right after making that decision to honor my parents, I had to go to downtown to pick up mom after I came back from a long hours of working. She told me she would wait for me in the front entrance of where she was and she wasn't there when I got there. I went into the building looking for her and couldn't find her. At this point I'm worried and mad at the same time. I called her once I came out and she was waiting for me at one of the parking lot entrances. I remember myself getting angry and trying to control my emotion by telling myself honor your mother as I'm on the phone. Then it dawned at me,.. it dawned at me what if this was not my mom but a new girl friend I'm going out with right now? Would I react this way as I'm reacting to my mom? Then I realized that there is issues in me that need to be dealt with or otherwise this will surface up and eventually will treat my wife this way as well. You see Noel, when you are mad at your mom even when you are right and she's downright wrong, it is an indication that there is issues in your life that need to be fixed. If you don't fix this, it will carry over to your personal relationship, i.e., your marriage, and you and your wife will have to deal with them together, which you don't want to carry over for it will definitely cause lot of problems. When God said to honor my father and my mother, it wasn't really about honoring them so they would be honored. But rather, the commandment is there for you to obey so you would be blessed through by honoring your parents. God's commandments or so-called rules are never there to restrict you from being free and take good things away from you but rather to make sure that you clear stay away from sinning and be blessed by obeying them. I believe I have issues that God wants me to be aware of and let Him fix it as I'm going through His loving discipline right now. If I have issues that stem from my parents because of their relationship, I'm sure you got issues that you need to face and deal with when it comes to relationship. You being 20, going through parents' divorce, and living situation will make much harder for you to honor your mother compare to what I went through.
I think it's a great news that both you and your mom are Christians. I know it's hard to understand your mom when she is selfish and whiny. But you, as a son, also need to understand what she had to go through with divorce and all. Trust me, there's no woman out there who does not want a happy marriage. I don't know the cause of the divorce (and whoever was the cause of the divorce is irrelevant) but I am sure she's bitter and vulnerable from that divorce, and not being able to have you when she split and all. You need to be the man in the house, whether she let you or not, by doing what you need to do without complaint and by loving her and honoring her. (Of course, make a constant complaint to God about your situation, emotion, rage and all... but not to your mom). One thing I can tell you from my small experience is that it will change you, and your mom will change to because of your change - the way you treat her by loving her and honoring her. The change has to take place from you first and it will spread to those around you.
Ahhhhhhh.............................. (a long sigh)
I know, I know it's not easy brother.
But I urge you to submit and honor your mother as much as possible.
I will pray for you not so your mom would stop being selfish and whiny but rather so you can stick to the 5th Commandment by honoring your mother. In that way, you will be changed, your mom will be changed through your life, and you will have a better and happier marriage with your future wife down the lane.
God bless Noel and take courage my friend.