Unprotected sex on birth control but then taking minocycline

I have been on Ortho Tri-cyclen Lo since April so about 5 months. I was a few hours late taking my pill on the 22nd but didnt have sex till the 29th but the 30th i took minocycline for the first time i asked a pharmacist if it was ok but then later found it that it can make a BCP less effective. I am not suppose to have my period till next Wednesday but this Wednesday i started having breakthrough bleeding and then a browish like color discharge/blood. I havent had this be4. Can it be a side effect of taking minocycline and the pill, just a side effect of the pill or can it be a early sign of pregnancy?

PLZ help i'd appreciate it very much ty