As uncomfortable as this sounds, it is normal. Yuck! These cramps are caused by prostaglandins that get released to help loosen the lining of the uterus and bring about menstrual flow. Unfortunately prostaglandins don't stay put in the uterus and instead go other places too causing cramps not just in the uterus but in other muscles too. If you are able to predict when your period is coming before you get your leg cramps, taking ibuprofen a day or two before may help lessen or prevent them all together. Why don't you talk to your mom or your health care provider about it and maybe give it a try!
That seems like an odd place for PMS cramps, but what I’m not a medical professional. Dr. Molly, our health expert, might have a more distinct answer for you -- but if this were me, or one of my daughters, I’d make an appointment to talk to a health care professional, if only to get some answers and reassurance.
I’m really not sure! See what our health expert, Dr. Molly has to say about this and if the leg cramps continue, see your healthcare provider.