I had sex for the first time 1 week and 1 day after my period. Then 2 weeks and 4 days later (the day my period was expected) I began to bleed. I thought I was on my period. But when I am on my period I usually start it in the morning and its really heavy. This time I started in the afternoon. This time it was light and it wasn't all blood like normal. It was also somewhat sticky as if it were semen or something. I looked up implantation bleeding but that was supposed to occur before the day of your period but not the day of. I'm really worried. I suspected it would be my period but now I am not sure... I have had no signs of pregnancy.

It may just be an off period for you. Periods are not all blood, there is often tissue and mucus as well, they just may not always be a noticeable. So one period can be different in appearance to another. They don't always start exactly the same either. It can be perfectly normal, for example, to be off a few days or have a lighter or heavier flow than usual.

Since you had sex, pregnancy can be a possibility and can sometimes be the reason for an unusual "period". You could try a pregnancy test and see what results you get. Be sure to follow the directions carefully.