Hi thanks for your question.
do occur after Depo shot .
You have not concieved from sexual act ,as your pregnancy
test is negative and your menstruation
occured after sex.
The sexual act was not unprotected since you are already taken Depo shot.
Abdominal cramps do happen sometime before and sometime during periods .There is nothing to worry.
You can use analgesic
antispasmodic drugs(pain killer) for pain and spasm.
Hope this answers your question.