Period question.. im a little concerned 10pts?

Im 17 n started my period at 14. They were alla over the calendar fromt he 8th to the 27 to the 20th etc. It only stays regular for about 5 months at max and then switches again. Recently its been coming aroung the 20th I havent had a period last month neither this month. I thought it idnt come last m nth becuase of anxiety and graduation stress. This month I have sore which is usually a PMS but still no period. Im not stressed or tensed my diet hasnt changed. im concerned why didnt it come for two months especially because i dont normally have skips