What Causes Prolonged Periods Despite Using Birth Control Patch?

I am a little concerned. I am on Ortho Evra birth control patch. I had a bad case of bronchitis last week and was on some antibiotics. I have not had a period in about 3 months, which my doctor said is ok, because I haven't been missing a week each month. I have been bleeding since last Friday steadily. It hasn't been as heavy as a normal period, and I haven't delayed putting my new patch on each week. Should I be concerned that I have been bleeding and cramping for 7 days?