I don't know if I'm really pregnant

Hello, my name is Krystal and I would be about 12 weeks along if I were pregnant. Since november, the time of would-be conception I've been worrying about being pregnant because it was the only time we didn't use protection, but I figured I was okay because I was on my period.. some signs that I've had is milky white excess vaginal discharge and my stomach seems to be growing, I'm not sure if I'm just getting chubby or pregnant.. and I'm a very petite girl. I've only missed one period... I had December's period but I missed January and now I'm bleeding again here in February.. I read that it might be spotting... but I just don't know any more because all the tests say negative...and recently I've had a lung infection and I had an X-ray and have been taking a lot of ibuprofen, is there a chance (if I am pregnant) that the baby could have birth defects? Can you help me?