No period for 5 months?

I havent had a period in 5 months I've had an ultrasound which showed nothing and I've had a hormone check with blood and it showed fine to so why am I not having my periods I'm 23 and they have been normal since I was 15

Jeff2019-03-14T05:05:39Z

Stress, excessive working out, or dieting are common causes. Call yoru gynecologist and chat with the consulting nurse.