Early Period!

I had unprotected sex with my boyfriend on NYE but he pulled out. I get water infections often and have recently finished a course of antibiotics for them about 4 days ago. About 3 days ago I started to see blood in the toilet after peeing and got scared that I might have a kidney infection. However, the blood is not in my wee as I have had the all clear from my tests! It seems to be a 10 day early very light period which I have never had before, but my breasts are not sore and I'm bloating a lot. I go through about 3 pads a day they are that light!! I'm really paranoid about pregnancy and just want to make sure that a period can be this early and what causes it to be so light?! X