Good Day I Had Intercourse With My Boyfriend About 2

Good day
I had intercourse with my boyfriend about 2 weeks ago. A week after intercourse I had my period. I am on birth control. I am on qlaira. In the last few days I have been really tired and I get enuf sleep so I don't understand why. I have some cramps in my back and tummy. I also get light headed really easily and it sometimes is so bad I have to stand still for several minutes. I do smoke and drink not alot but I do and in the last few days smoking or drinking makes me sick. I do have a yeast infection and heard that early pregnancy can cause this Ihave my first year exams on there way so could this be because of stress or might I be pregnant?