Can anyone hep with this?

recently my bf and I had a bit of accident and were both worried that I could be pregnant.this accident occured sometime n jan.(I had my period)however,feb my period ddnt show up.march my "period" came but it was very weird.I ddnt have any cramps(very unusual)my flow went frm lite to heavy.I took a pregnancy test(I've tken alot)bt their all (-).I was on bc,but only 4 a month becus I had problems gettin mre.(I hvent been on it since)I'm wonderin if I still could b prego or maybe the bc messed me up?