Late Period. The reason for no period?

Dry humped on day 5 of period. He was wearing underwear and cargo shorts and I was in my underwear and pajama shorts. I also had a sanitary pad on since I was still bleeding. He didn't ejaculate, only precum. Period was late by 2 weeks and negative pregnancy tests, so took meprate for 5 days, got periods 5 days after stopping meprate. Then got a period again within 7 days after last period ended. Heavy bleeding, clots and cramps. After this period ended, got transabdominal ultrasound done for irregular period. It says "poly cystic morphology" endometrial lining 6.69 mm. This was about 10 weeks after the dry humping incident. Got next period 25 days after the last one. Now period is late again this month. Can I be pregnant from that incident? No sexual contact apart from that incident. What is the reason for no period?