I have a question medroxyprogesterone!!

I have been taking medroxyprogesterone this would be my 3rd period on this medicine I started with taking 14 days on 14 days off I finished my 14 days on the pill on the 9th of December I usually start my period a few days after I stopped the pill and it is the 15th now and I have not started my period I been having cramps that come and go I've been having like a little bit of milky white discharge and my vagina hurts my boobs hurt but my boobs hurt when I first started the medicine but then it went away but now it came back... Has anyone had this happens while they were on this medicine?? I took a test on the 9th and it was negative but I don't know if that was too earlier... but some people say you can't get pregnant on this pill then other say you... since I've started this medicine my periods have been doing pretty good besides this one is taking a little longer what do you guys think??