What could be the problem .?? Please help!?

Im going to keep it short. My period was supposed to start on the 20th its now the 24th. Yesterday after i urinated and wiped there was bright red blood on the tissue so i put a pad on and there was a little bit of blood. I changed pads and a few hrs later there was nothing in the pad but when i wiped there was bright red blood on the napkin and a little darker red drop. That repeated one more time then nothing again. Im cramping and my boobs are sore. Idnt thnk its implantation bleedig though. What can you tell me is going on?? Thanks in advanced .!