Birth Control

Patient: Hello.I have a question,please answer soon!So,I had sex 9 days after my period was over.I took 2 birth control pills after the first time,but after that I had intercourse twice.And I didn’t use my pills anymore.It’s been one week after I had sex (about 15 days after my period),I feel tired and My tummy hurts,The place where it usually hurts when I’m on my period.I thought I was pregnant so I took a pregnancy test yesterday and it was negative.but still,I started to take pills.Even though the test was negative,I still think I might be pregnant.Is it possible?Or these symptoms are only because my ovulation has started?P.S. I think I might have my next period in 2 weeks or so.Thank you.