Could I be pregnant? Please Advise?

I am on the Yasmin pill. My last period didn't really appear to be much of an actual period. More like spotting. I had some serious nausea and abdominal pain towards the beginning of me starting to take my pill this month as well as an upset tummy. I've been told having diarrhea and sickness can affect the absorption of the pill. I was also on anti b's for YET ANOTHER urinary infection so the effect of the pill would have been lessened then also. I'm not overly reliable for taking the pill. Doctors did a pt when I was prescribed the anti b's which was during week 2 of pill and it was negative, but not having the usual symptoms in the run up to me coming on as I normally do. I was just wondering how likely it would be that I could be pregnant?