Answer:
Cramping is hereditary so it doesn't matter what your size is. My sister had bad cramps and she was chubby.
Cramps are not determined by your weight but by other factors - hormones, etc. However your body could have a tougher time dealing with your period if you are significantly underweight. I would schedule an appt with a GYN as soon as possible, or even your regular physician. Ask them about the cramps as well as your weight.
well im like the same age and weight and height as you and am nomally fine .i dont think it matters if your skinny or not.