Dumb question

I'm having some light bleeding, I'm not sure if it's implantation bleeding or not. My question is, when could I take a pregnancy test and get accurate results, if this is implantation bleeding?

I'm on the pill but last month my pharmacy ran out of my kind and gave me another similar pill. Then this month they gave me my normal pill again, I didn't wait a week after starting the different pill or my normal pill this month. We had sex without a condom and he just pulled out (which obviously isn't a reliable method). So because I was switching pills, I'm not sure if it's implantation bleeding or just normal bleeding from the pill (not my sugar pill week)