I've been reading all these posts about implantation bleeding and it's got my mind racing a million miles a minute wondering if thats whats happeend with me.

I had been on the 4-periods-a-year-pill for about a year now. I had breakthrough bleeding in mid june, and had my normal period in late june. I stopped taking the pills once that set was over at the beginning of my period because I had gained weight since i started taking them, and wanted to start trying to lose it. I had unprotected sex in the last few days of june. it's now july 11th and i noticed brownish/pink discharge today. could this be from stopping the pills or could it be implantation bleeding? when should i take a pregnancy test? please help, because i'm completely clueless to this kinda stuff and would like opinions from people who have been through it. thanks.