Tell Satan to leave you alone. He'll fight you at first but eventually he'll listen.
The psychological cause is that your brain is developing into an adult brain. As it does, new areas open, and you can see more things. Satan has seen a lot of people grow, so he knows what to tell you to think about to block you from seeing what God wants you to see. God allows it, so that you will come to Him, give Him each new brain area, and fill it with His thoughts. If you refuse to listen to Satan, and ask God what to think, that will solve the problem.
Since you are newly saved, let me also mention: God starts out giving you great feelings of how much He loves you. Then, after a while He takes the feelings away so that you will grow to love Him by faith. Act on what you know to be true, think on things that you have read in the Word, or you know that are good, and realize how you feel does not matter, since you will live by faith from now on. This is all part of getting over that hump from joyous early salvation to mature Christian.