Can this breakthrough bleeding mean I am ovulating?

I have read on MANY sites that Fioricet interacts with Yasmin. I had no clue until now. I started having breakthrough bleeding (taking pill PERFECTLY for 4 months), so that is why I looked up the interaction. I was on antibiotics for a kidney infection and got my period 2 days early, so I stopped the pills since I only had 2 days left. My LMP was around December 15th. I started my new pack on the 20th so that I could get my body on track from having an early period. I had a normal period. It wasn't lighter than usual or anything. I have been taking Fioricet for cluster headaches for 2 weeks and just finished the prescription on Thursday. Last night, I started spotting and still am. It picked up slightly, but not like a normal period. I guess my question is, how likely is it to get pregnant in this situation? Does breakthrough bleeding decrease the chance that I am ovulating? I read somewhere that medications containing butalbital, increase the chances of pregnancy on birthcontrol by 25!! Seems like an aweful lot huh!? I am nervous about this! My fiance and I had an "alone" night last night, which makes me more nervous. Had I known about this interaction, we would have used a back-up method! The Dr knew I was on birth control and never said a thing about an interaction! I knew to be careful about the antibiotic, but no idea about this! Thanks for anything you can offer! Personal experiences, advice, ANYTHING will be great!