[Dark-and-Twisty]

If you've had your period since you've had sex, you're not pregnant. Sperm dies very soon after it hits the air, so the chances of you get pregnant from it being on his finger is almost impossible. I would say relax. You took a pregnancy test and it was negative. A lot can cause weight gain: ie, stress, eating more than you used to, ect.

But it's a really bad idea to lie to your doctor about having sex.