What Causes Prolonged Vaginal Spotting While On Depo Shot?

Hi I had been on depo before like 2 years ago for a year and everything went good. I got my shot from a clinic with my local Hospital. At the beginning of 2015 I got the depo shot at my school (I moved to a different sate) . The first time I got it was a day or 2 after my period as before and everything went fine I had no periods a lil spotting at the end of the 12 weeks . This time she gave me the shot the 31 of May while I was on my period and I haven t stopped bleeding since . It s been plenty of spotting everyday randomly and bad orders. Baths won t even work. Idk what s going on but I m not going to be getting this shot again from my school.