I feel sick but haven't been sick

I am 15 I'm on the pill and have a sexual relationship resantly iv been having really bad stomack pains in my left and right side of my stomack, I have back ache mostly in the middle of my back I feel sick but haven't been sick, and when I urinate when im near the end I get a sensation that makes me feel like I still need a wee. im due to take my last pill on sunday, but me and my boyfriend are worried I could be pregnant, what's wrong with and could I be pregnant? Please help