Hello
firstly no-one on here can tell you defiantly that you have AvPD or SA. you should check out the criteria for these and see if they fit you
AvPD=
http://en.wikipedia.org/wiki/Avoidant_p ... y_disorderSA=
http://www.helpguide.org/mental/social_ ... atment.htmas for people with personality disorders not knowing they have one, i think it is that while we feel it is normal, we see that other people (generally the majority) act differently to us, so we decide to see if we have a problem (why i looked anyway).
some of the things you said come across as AvPD (thinking everyone is talking about you, fear of rejection) and some as SA (eg you can talk to people and open up). however don't try to label what you have because you might sub-consciously go down that path (what i am doing

also 19

). would recommend seeing a psychiatrist if you feel something is wrong, however keep in mind that not every shrink is good, so if you don't like one, find another (what i'm doing)
hope this helps/makes you feel better in someways
Constant dripping hollows out the stone. Lucretius