Can I do gym when I have my period ?

You most definitely can do everything just the same as if you weren't on your period, you just may have to make a few adjustments. If you have a locker, keep pads in there. Chances are no one's gonna care if you're on your period because they're all girls in the locker room and I'm sure they'll understand. You can still run and do all that while wearing a pad, it just might be more uncomfortable if your period is heavy. You can always try wearing tampons, but if that makes you uncomfortable just stick with pads, get the thin ones with wings and the longer size to assure no leaks. Maybe you can make a quick stop at the bathroom right before gym and put a fresh pad on. Also if you're comfortable and if you have a female gym teacher ask if you can keep some pads in her office. If not, you could even ask the school nurse and stop there before class and put a new pad on. You might think it's embarrassing to ask the nurse or teacher, but I guarantee you they will think nothing of it and they will be completely understanding. If they are women, they've been through it too and know how it is.