Getting sick everytime I eat?

I'm 18, I weigh 130 lbs, I'm in pretty good health. I had a blood clot at 15 from a birth control pill and was on coumadin for a year, and I had my gallbladder removed due to pain when I ate sometimes. Well, I just got on a new birth control, Implanon and so far so good. I'm having breakthrough bleeding right now tho. Anyway, I have rly frequent UTIs and my urologist put me on an antibiotic for 3 months and the pills have helped me SO MUCH, I'm almost done with the first month's bottle, the medicine is called Macrodantin, 100mg. And my mom seems to think the pill is what's making me sick when I eat. If I don't eat anything when I take it, I throw up. I threw up so bad from it one day it lasted two days! But also, it seems like when I eat something with it..it also makes me kinda nauseous and I end up feeling like I need to throw up for relief. Is this medicine usually hard on the stomach? He upped my medicine to twice a day because my urine culture came back with bacteria..so I take two a day for a week..then continue for the next two months with it once a day. Idk if it's the medicine making me sick or if a bug is going around?