I'm 15, not ually active but taking birth control and I've had my period for 18 days now. I'm confused..

I've been sick on and off with common cold symptoms with "Hints" of bronchitis (sp?) thrown in there. a few days into taking the pill, I started to take an antibiotic, Erythrocin and continued 3 times a day for 10 days. All during that time, I had my period. I thought it would stop 10 days later... but it didn't. and its been 4 days since I've emptied the bottle. I'm getting sick again with bronchitis and congestion and blah blah blah. I've been looking online and found nothing. I'm stressing out because I started taking the pill to "lighten things up" But I'm just stressed. =( istance si vous plait.