What Causes Jel Like Discharge And Abdominal Cramps Inspite Of Taking Contraceptives?

Hi I am 21 years old and I just started birth control this month. I am on my last week of it. My boyfriend and I do have sex. he does not wear a condom. We had sex in the very beginning of me taking my birth control. Since I ve started my birth control in the beginning I would have really bad cramps and felt really sick. It lasted a few days. Friday I started my period and it was the lightest it has ever been. tomorrow will be the last day for my period this month. Today when i was going to the bathroom and i wiped there was this stringy jelly like thing on the tissue. It was not discharge at all. It was jelly like and clear with some red. What could this be?