Why haven't I gotten my period yet? I'm already turning 17!?

Well, I'm 16 turning 17 in early October...and I'm obese. I've heard that heavier girls get their menstrual cycles early because their body is able to carry a baby. I'm definitely overweight and I'm 5 foot 7 inches. If you need my exact weight it is 245. I know, that's horrible, and I'm changing it, I use to weight 253 but I've been exercising and beginning to eat right. It is just awkward when all my friends and girls younger than me talk about their menstrual cycle, and I haven't had mine yet. Also, I do have pubic hair, I've been getting it for about 3 years now, but my legs are rarely hairy, I legit shave about once every month...or even less. My are average I guess, they're a C cup. I've definitely rounded out getting curves, but then again that may just be from my weight. I really want to kow if there is anything wrong with me. My mother got hers when she was 13...older sister 8..and other sister 15 << although she was veryyyy skinny until about then... I would love for anyone's advice...am I abnormal.?