Skipped a period

I am 24 years old and never in my life skipped my period. I am nervous because of my hot flashes and everything. No possible chance I could be pregnant at all!! A few months back I told my OB I felt like I was going through menopause and she laughed and told me I was too young. Now I’m worried her not looking into my problems I may have one? I can’t even sleep with the hot flashes and I’m also have extreme mood swings. Last month my period was like a day which is extremely rare for me as well and now completely absent. Help?