What Could Cause Menstrual Irregularity?

hi! i am 35 yr old,my height is 5ft,my weight is 66kg.i had normal delivary 10yrs ago.i always have a regular period cycle(between 25 to 30days).last month i had period on 19th march,2014.today is 27th april2014,till now idont have my period.last month i have taken i-pill,this april month is very stressful as my son was ill.yesterday (26th april) i have done pg test through kit,which come negative.today i have gone to my gynecologist,she checked manually ,found negative,she advised me to do again pg test if negative then to take primoult-N ,3 times aday for 3 days.she told me if next month also same situation arise ,then to go for TSH,CBCC ESR,ultra sound of lower abdomen.but i worried if i wait for next month,isn t it too late?