Hi Rizarita, Depo is a pain! Some people do believe Depo can cause infertility, however there is no evidence to support this, and infact if you ask any health practitioner they will tell you that Depo doesnt cause infertility. It can however take a loooong time for your periods to get back to normal. I have the same symptoms as you, but mine occured after stopping Depo. I would suggested going to see you doctor who can help.
This happened to my sister after she was on depo for ~5 years.
I suggest going to see a gynecologist who will help you decide what the next step is for you.
My sister had to stop depo, but she still bleeds nearly non-stop.