Is this a withdrawal bleed?

I have been on birth control for 10 months now without any problems. I am on my second week of my birth control pack so I am on my active pills. I am two weeks away from my period and I am bleeding as if I were on my period, plus having some clots/brown tissue coming out.. Is this normal? I am sexually active but me and my boyfriend use a condom every time plus sometimes even with a condom on he will pull out. I started antibiotics (amoxicillin) for my sinus infection a little over a week ago and I finish at the end of the week so I’m not sure if this is the cause of my bleeding? Could I be pregnant? Thank you for your help ladies!