Last month (march) I wasn't on birth control. I had been on it for months, and just didn't get my prescription in time. And stupidly, had unprotected sex.
I did get my period, it was 3 days late, only lasted for 3 days and was extremely light.
Then I got my period again on the 15th. There was slight spotting on the 14th, then after intercourse, it was here fullforce. Now I still have it, it's been 8 days.
I'm not supposed to have my period until the 29th.
Should I be concerned? Or was it just because I missed my birth control last month?

MIssing your birth control shouldn't make you bleed at all. It just makes you more fertile. If you have irregular periods then you might have had your period early. Here lately I've been spotting a day or two before my actual period starts. Intercourse can bring on your period if your body is trying to go through your cycle. And stress or other factors can make you have a longer period. I've had a period that was 10 days before. Just take it easy during your period and drink plenty of fluids and it should help.