What Causes Missed Periods?

Hi,I have 25-26 day cycle everymonth,never I had irregular period.This month I missed my period and on 31st day I had a home pregnency test, but unfortunatly that came negative.On the same day follecular study shown endomet 6.7, right overy msf and left overy raptured.today is my 35th day till now I did not get my period.I am taking Gestone 200mg from 33rd day.Iam trying to conceive from previous 3 years.I am in hope that I am pregnant.please suggest my pregnancy can happen this time?What is the meaning of that folecular study taken on 31st day?Please reply.Should I continue my hope? my age is 35+.