Help??

So I'm currently on birth control, I've been on it for a few months now and for some reason recently I've just been really bloated, like it feels like I'm full of air. Then I'm really nauseous a lot and I've had bad cramps off and on. I had my period the 15th-19th (its currently the 29th) so literally a week or so ago. Since then, anytime I've had sex, we've pulled out AND I'm still taking my birth control regularly. Ive taken 2 pregnancy test since my period and both were clear negatives. What is going on??