Hya,
I had unprotected sex 1 day before I started my period. When I started it was very light, but I'm usually quite heavy.
I've been having headache and lower back pain. And I'm just waiting for my next period to start.
Is there a chance I could be pregnant?

I believe that you are not at high risk of getting pregnant the day before your period. The highest precentages are 14 days after your last period. This would be when you ovulate... you can also get pregnant as far as up to two days after that. Don't stress until you actually miss your period. This can very well cause a delay in your period. I know this happens to me every other month... I start thinking I'm pregnant and my period delays two days.

Hope I can be of help - It is possible for you to be pregnant even if you had sex 1 day before your period. Sometimes more than one egg can be released whilst your body prepares for menstration or conception. It seems more likely that you are not pregnant and just having a lighter than normal period. If you are worried and/or stressed, the body can react in many ways - including headaches and other twinges. I personally would have a pregnancy test and I feel that it is very important that you see your doctor - the lower back pain you mentioned could be due to an infection and even if you are not pregnant and dont have an infection, its better to be safe than sorry. You didn't say your age, and, if you are worried or not about the chances of pregnancy - If you have someone close to you whom you can trust and speak openly with, without being judged, I'd have a chat with them - I hope my answer has been of help - Regards