Unlikely to be an STD for sure. Bleeding after sex the first 2-3 times is quite normal, so since you say it's getting relatively lighter, I wouldn't worry. If it continues too much longer without another session of intercourse, I would get checked out, but so long as it continues getting lighter, no need to be concerned.
It is getting relatively lighter . It was never actually very heavy it's just been consistent . We were both virgins so I don't see how it could be an STD.?
Is it getting lighter? If it's not getting lighter or you have not had your second time since 11/18, I really would get to a doctor. Your health is more important than hiding this from a parent. If you live in a state or country that allows 12-year-olds on up to make and attend appointments without a parent, take advantage of that and make an appointment then ask a friend's mom if she can take you.