Worried jfc

Basically Been on the depo shot since Nov 4th 2015 and I haven't had a period since December, just discharge that the doc said was normal, I'm due to get my next shot on April 20th but I've just started bleeding kinda heavily and there's clots, so I'm really worried? I have had cramps for the past few days, could it be because I started antidepressants two weeks ago?