Hi, and sorry if everything i'm going to say will look a little funny but I can't seem to get over it. 

Last time I've had sex with my girlfriend was almost 2 months ago, between April and the beginning of June. We were protected but we did use the pull-out method a couple of times (i know, stupid thing to do, i tried to take all precautions like urinating beforehand and i was never near to orgasm when i pulled out, didn't actually enjoy it) 

Anyways, I've read all the stuff on the Internet about how the pull-out method doesn't work at all and I developed some kind of constant fear that she might be pregnant (yep, me, the guy). She's been having regular, heavy periods all along, with cramps & everything, but her stomach started to get somehow bigger in the last couple of weeks. I told her about it and she laughed at me telling me that I'm paranoid and that I have nothing to worry about. She told me that she is getting fat because she ate a lot during her exams and because of her thyroid operation in January her metabolism is screwed up.

She doesn't feel unusual at all, no pregnancy symptoms, and doesn't even want to take the test because she keeps telling me she's not pregnant. But I still keep looking at her "enlarging" belly and becoming more and more anxious about it, mostly because I've heard all those stuff about how you can be pregnant and still have your period and no symptoms at all. 

Now, the question is, should I keep having my concerns or stop thinking about it as it all might be something in my head?