I was on the depo provera shot for a year in a half and I got off it about two years ago. Since then I've had one light period and it was a slight brownish colour back in July. I had unprotected sex about nine days ago and three days after I started spotting and then it started to get heavier and hasn't stopped. I should also thrown in that I hadn't had sex in a year before I had the unprotected sex.

My question is, why is this happening all of a sudden? It doesn't make any sense? Could something serious have happened? His penis was not that big by the way...

Sadly there's really no way to answer this online. We don't know your medical history, we can't run tests, we can only guess, and guesses aren't at all valuable.

It's time to see your doctor.

Good luck. :)

In doing some reading, I find that women do complain about this a lot. Of course I don't really know if they represent a high % overall, or just the ones who complain. But it is known that irregular bleeding is common, either while getting the injections (often bleeding stops altogether), or after stopping, when women tend to bleed more.
I found one blogger who said that her doctor had to put her on the pill to regulate her bleeding, after going off the shots.
So far, you have been bleeding about the number of days (6? not clear) that is within the range of normal.
BUT MAKE THAT APPOINTMENT NOW, in case it continues much longer. And in case it's something totally unrelated to Depo!
Two years seems out of the norm for heavy bleeding to suddenly start, even though the disruption to hormones from Depo lasts quite a while, but usually measured in months.