Period a week early. Started after Sex.

Yesterday, my husband and I had sex. It was not rough or anything. I was sore afterwards. I have been with the same man for five years.

A few hours later I had bleeding like it was my period. My periods have been very "off" since the beginning of this year. It went from starting every 27-28 days to 33-34 days. Which I have been told can be normal, especially if you are under stress. Well this week it came at its usual time. It feels like a period. But I'm worried that it was from sex. I have a copper IUD and have had it for almost four years. Never had a problem with it. Could it possibly be something to do with that? I am having no other problems other than my period came a week early.

Thank you