lower mid back pains

i just started the bc shot , it stops my periods but ive only been on it for abt a week. the day after i was supposed yo start my period and a couple days before my period i get cramps , throw up , and get dizzy spells. well today at school i was getting some lower mid back pain and it was the worst. and about an hour ago i had it again but it was also shooting forward to my ovaries then down. it hurt like crazy i thought i was abt to drop dead and die. but if anyone had ever had this before and knows what it is can you let me know?