My girlfriend and I had intercourse about 3 1/2 months ago she has not missed any of her period or had any symptoms of pregnancy, should I be worried? Because I've heard of so many stories of people not knowing there pregnant until they were 6 months into it?

You don't have much to worry about, her periods are regular, so that means she's ovulating, all signs point to no pregnancy. Couldn't hurt to visit a doctor or take a pregnancy test or two.

You probably shouldn't worry but why not ask her to take a HPT to be sure?