Hi there yiamdi, and welcome to Scarleteen.
It's very common for bleeding or cycle irregularities to be a side effect of emergency contraception. We can't know exactly what's causing this bleeding, of course, but it's very likely that what you're experiencing is a side effect of the EC. What we do recommend for anyone who takes EC is that they go ahead and take a pregnancy test once one would be accurate (the packaging of a test will tell you when that particular test will be effective), so that's something you could do to ease your mind a bit. I also want to give you the link to our big roundup of
pregnancy scare resources for further reading; hopefully having that information will help.