Pregnancy, need answers!!

I'm 18 and yes I don't use protection at all, I don't need anyone to call me stupid or irresponsible, I recently had a sharp pain on my left side it was kinda constant though a day but then bleeding started, it ended. This was about 2 weeks after my period. I just wanna explanation. I've also gained weight! I'm a small girl, I usually weigh around 93-97 but I'm 107.I've never been a hundred at all. I have thrown up a couple of times in the same night, I'm not sure if it has to do with it. I'm gonnaa buy a test tomorrow hut I need answers now...