I totally get you. I am actually a pretty social person overall, yet I still catch myself just lurking a lot of the time. When I started up on ZB a few years ago, that was the first forum I ever became really active on, and that took me like a solid year of lurking first. I found that at a certain point, if you wanna start joining the conversation more just dive in! I almost had to force myself to post a few times a day, at least to start out.
That's pretty much where I find myself now, forcing myself to post.... then I spend an hour worrying over how useless the content probably was hahaha I'm terrible! >.<