How soon after intercourse can implantation bleeding occur?

I am on birth control pills but I will be honest and say I have not been taking it at the same time every day. I try to but sometimes I'm busy doing something and forget for a few minutes to a few hours. Ok i can't remember the last time I had intercourse but I know it was about 2 weeks ago. But I have been had some vaginal spotting of a pinkish red color twice in the last 24 hours when i wiped.

I still have another week of pills before my period is due. And the last week I have done good at tasking my pills At correct time. It is not normal for me to spot on the pill either.

I took a hpt test this morning and it was negative.