U don't need to wait for your periods but Do your urine pregnancy test once and if in doubt, do one Usg also to rule out pregnancy. Then u can go for Depo provera injection. But u must know few things. This injection may sometimes lead to irregular periods or spotting. If you face this side effects, u need not worry much. Also, long term use of Depo provera cause osteoporosis. So limit it's use for upto max 1 year, though the bone loss gets  recovered after stopping it

ARE YOU AWARE THAT DEPO PROVERA WILL STOP YOUR PERIODS TILL YOU R ON THE DRUG. THE BEST OPTION FOR YOU WOULD BE A COPPER T. IF YOUR ARE COMFORTABLE WITH COMPLETE AMENNORRHEA THEN YOU CAN OPT FOR DEPO PROVERA

Hi,If you opted for depo provera, you can either start at 5th day of period or can start after confirming non pregnant status by ultrasound and if required upt and or beta HCG when in doubt. Not necessary to wait for the period.