Don't diagnose yourself. I also did that. I sometimes think I have AvPD, sometimes I think it is just low self esteem, caused by childhood traumas.

Try to find something you feel you are good at (or not bad). If you can't, chose something and become better (exercise, some are of knowledge, whatever). Study or practice until you feel you are comfortable, then maybe talk on some forums and then try with someone in real life.

And go to a specialist for diagnosis.