Am I pregnant?

I had sex with my boyfriend on July 22nd, and neither of us was wearing underwear. He didn't ejaculate inside me. Two weeks later, I got my period, but normally it lasts 5 days, and this time it was only 3-4 days. My mom said it could be due to climate change because I had just returned from vacation. A week later, I took a pregnancy test, and it was negative. Could I still be pregnant?