What Causes Delay In Periods?

Hello Doctor,

I am Preeti Sharma(Female), Age:29yrs . Last year in month july i had my D & C done as doctors said that baby was not growing and will not grow also. No again we are trying for baby. In febuary my periods were just 4 days long(normally my periods are 7 days long) then in march and april also it was 4 days long. but in may it was just 3 days long, infact 2 days thats it. Now in this month that is June my periods has not started. LAst day was 23rd may 2010; and today is 21st, cycle of my period is 28 days accordingly i should have my periods.
My question is I am i pregnant? and is it normal that days of periods get shorter?

Thanks