implantation bleeding?

I wasn't supposed to start my period till the 8th. I was on the implant for 3 years then switched to the pills for two months and this is going on my second month off of any birth control. my fiance went to grab me last night in my abdominal area and I had bad pains. ok went away and we did the deed. this morning I woke up to dark blood but absolutely no clots or anything or pain. I did read online that there are some women that have heavy implantation bleeding? I am just wondering what could be happening. please let me know