I get suspicious if a girl shows clear interest in me.

If a girl acts overly nice to me and flirts heavily (such as touching me, hugging me tight and close and holding me, giving me kisses) I get suspicious. I don't really get attention from girls, never had a girlfriend before or been on a date, still a virgin. If a girl is forward like in the way I have just mentioned I get suspicious. I always think she is up to something.

What could be the cause(s) of me thinking like this?