pregnant or sick?

So I recently let my boyfriend cum in me, and I have before in the past and I got my period. I am on birth control and have never missed a pill or taken it more than three hours after or before my selected time slot. About a week and a half ago, after my period ended, my bf came in me a few times and then I went to the beach on Friday. I've been very nauseous all week and just feel weak. It's not all the time but I started feeling like this the second day I was here. Is it possible I'm pregnant? Do symptoms occur that fast? Or am I sick from being exposed to heat/or just sick in general?