Confused 🤯

So I’ve been on cezerette for 30 days now I was on micronorgn before never got a period so my doctor told me to just start on cezerette straight away which I did, so I bled from the end of January till about Feb the 12th still taking the pill daily routinely so me and my boyfriend had sex for the first time since I swapped over due to me bleeding on the 16th of Feb I now today the 24th had a strange moment and a little brown blood and fresh blood then it all stopped but had been having cramps for a few days like my normal period cramps I get them down my legs etc I’m thinking implantation but I take my pill between 7am & 8am everyday and you get a 12 hour window so what the fuck is going on I cannot possibly be pregnant before any birth control I was a 28-30 day cycle