I’m having the exact same problem, I was on the shot for a year and didn’t have a period until a year later and my periods are off and on.
That sucks. I've heard this was a possible side effect of the shot, which is why I've never gotten it. There's not much you can do since it's not like the pill where you can stop taking it. Unfortunately you'll just have to ride it out until it stops. I'm sorry you're having to deal with it though. You definitely have my sympathies.
You could double up on contraception it will be a hassle but if you take the contraceptive pill aswell as the shot it can help regulate bleeding