Starting the pill again

I had gone off the pill (big mistake I know) and I had a sexual encounter where I thought some cum could have gotten into my vagina, so I took EC two days later, I started bleeding on my expected period day but it seems a little shorter than my normal periods. That following Sunday I started back on my birth control and I'm also on antibiotics, I just went to the bathroom and there was like a dime sized amount of blood on my panties, is this normal? What could it mean? I also worked out yesterday for the 1st time in a few months so idk if that has anything to do with it.