Warning!!!! TMI!!!!! Blood shot!!! I have an implant fitted however have been experiencing spotting

I've had the implant in since October now since having a miscarriage and I haven't bled since then, however on Monday I experienced some cramping and back pains as well as spotting, at first I thought I may have been on my period but was unlikely as I haven't bled since having the implant fitted anyway it wasn't in any shape or form a period as I used to be very heavy on my period it was just a little pink/brown mark on the paper, I've been absolutely knackered this week and have had itchy nipples but I didn't think I could get pregnant on the implant?