Physically speaking:
Your brain operates on Pleasure/Pain-----every motive of you operates on this from what you eat to what you wear to what you do.
Not that you have to mention on here but, what in your past can you write down that may have caused this insecurity, shyness, or SA??
Then try to see if you can write down how you can fix this objectively, there will be practice before perfection if ever perfection is acheived.
This symptom can be one thing but the solution lies in the root.
Your condition is near and dear to me.
Do you?
Want to be liked and scared that someone may not like you?
Are you insecure? And if so,, search yourself and find out what about.
Conclusion=
Most SA goes away when you learn to develop an attitude of loving yourself enough that no matter what someone else thinks or feels about you, you are still Happy with yourself in a manner of speaking. I can never be totally happy with myself as there is always much need for improvement.
Also, when you pray,,,, most times God answers our prayers by presenting circumstances for us to handle our problem. So if you pray for this to go away chances are God is going to present you with opportunity to overcome this thru "action".. Be intentional,,,be purposeful,,,make yourself say hello regardless of how many reciprocate. When you get comfy with this move on to the next level,, say hello, then ask how they are doing to the ones that respond.
Make it a game, if you really want to have fun ask the ones that dont say hey back how they are doing today.. If you want to get serious about it,, put yourself out there and the ones that look upset that you said hello, stop them and look them in the eye and ask them if everything is ok and tell them that you hope it works out for them or whatever you are led to do.
These intentional acts can create a totally new paradigm for your life!