Birth control depo shot?

Im due for the shot on the 31 ... Im getting it tomorrow the 30 last night i had sharp sharp cramps ... Bleed a bit/spotting this morning ... Still having the sharp sharp cramps and spotting .. Is it normal .. Is that ok ... And also what is the best for stretch marks i have them on my inner thighs and on both sides completely ... I've gained so much weight so quickly from this shot