My Age Is 23, My Periods Is Last Normally Com

my age is 23, my periods is last normally com in june 2016 agter that my periods is not comeing in july as wll as august when i consult the doctor she advice to take DEVIRY 10mg teblets i take 3days that in august my periods was come as normal but after augest my periods was not come i take Deviry 10mg teblet 5 days but there is no result what can i do