Pms or pregnancy?

Hi I am on birth control and I haven’t missed a pill. The last time I had unprotected sex was December the 1st. I am on my second placebo pill for this month and my boobs aren’t sore but have sharp pains, and they are tender,but it only happens in one at a time. I have a lot of gas and I have been wanting to eat everything in site. My period is supposed to start soon, and I am worried. I took two pregnancy tests and they were negative. can you help?