What Causes Stoppage In The Menstruation?

hi, i am a 32years female.I have one son who is 2 1/2 yrs age.I have conceived with IVF therapy.Post delivery I had got my menses after my baby was 5months old.But later there has been gap of 3-4 month between two cycles and now since year 2013 i am not getting menses.My gynaec had checked my hormone levels which were normal and given me Modus stimulation, with which I had menses lasting for 20 days(this was in Jan 2014).My USG report was normal as per gynace.Have i attained early menopause? Till 2013 i used to get white discharge, but since Jan 2014, there is no white discharge.please help.