Weird periods

I'm on the depo shot. I've been on it for almost 6 months now. My first period on it was really heavy and it lasted for two months. Then, I didn't have it for a while. It came back this time and was normal. Then it started to get really light, with barely anything on my tampon. I started bleeding again for a couple weeks. Then, it started slowing down and then stopped. A couple days after it stopped, I started noticing "old blood" that came out for the next few days. I sat down the other day and wiped and there was blood. So now I'm bleeding AGAIN. Idk what is going on.