Is it possible for a woman’s menstrual cycle to change after she becomes sexually active? Experiences?

21F, I had sex for the first time with my boyfriend (22M) on February 3 and February 14. It was protected—we used a condom, and I asked him if it slipped during the act, and he said no. He also used the pull-out method. My period was supposed to come on February 28, but I ended up being 9 days late and got it on March 9 instead. The bleeding was light but had clots, and it lasted for 8 days. My usual period only lasts 5 days. Now, I was supposed to get my period on April 7, but until now it still hasn’t come. I’ve just been having lower abdominal pain and breast pain. I also took a pregnancy test on April 6, and it was negative. Is it possible that my cycle got messed up because of what happened? I’m very anxious about this. My lower abdomen has also been hurting for about 2 weeks now. Note: After my pregnancy scare in February, we didn’t have penetrative sex again because I got really scared. Around March 24, I took another pregnancy test to be sure, and it was negative. Then again on April 6, still negative.