Help!

I had sex with my boyfriend on September 6,2014. I had my last  period 5 days before that date. I am just now becoming sexually active, I am still yet to have a period. I am too young for a baby and I wouldn't be able to give the baby the life it deserves. We agreed to not have sex again until we are older and can support our child. The only possible way I could be pregnant is from his pre-cum. I haven gotten a lot of mixed response on this topic but I need the clarity. He simply put it in for 4-5 strokes and we realized that we were making a mistake and stopped. I took two pregnancy tests on October 16th and have gotten negatives. I am experiencing no symptoms at all. My period has never been regular but it managed to come. Please help.