Plan B, Did it fail?

My period started being screwy during the summertime months, I was getting about two a month. I saw a doctor and he told me I should be fine once swim started, and I believe he was right. I had a short period from about the 3rd of September until the 7th of September (did not have one in august that I have recorded since I got a new phone...but I believe I had one at the very beginning). Anyways, the seventh of september I had unprotected sex...I do not believe he went all the way because I had ended it early, feeling really uncomfortable with the situation I was in. Anyways, I went out and bought plan B the next day, took it. The 13th of september I started my period again, it was red and I needed tampons for about 4 days. I have not started another period since. It's october 15th.....Should I be really worried? I'm starting to feel really sick to my stomach about this....