Period problems

This might be a bit TMI but I got the implant out on the 28th of September and I went on the pill on the same day, I thought that my period would become regular again after getting the implant out because it wasn't regular with it in but I have had no sign of my period apart from some cramps now and again, does anyone know why I haven't had my period since starting the pill? And just for reference my last period was end of July into August and it lasted for like 3 weeks which is weird