Why are my periods lasting longer after I got the birth control shot I was on my period for about 8 days then a week later I got it again.. Why

It takes your body a long time to get used to the new fluctuations of hormones that any type of birth control gives you. If the injection was a high dosage, it can cause more frequent and longer periods for the first couple of months until you become regular. Even then, your periods may last longer, just they may come less frequently. If you get on a lower dosage, you can get less frequent periods and short ones. Talk to your doctor about your dosage.