What Causes Delayed Periods While On Treatment For IVF?

hai i am Mrs.sharmila ,27 years,married before two years we r going treatment for baby.for both basic test r finished all r normal..... cycling of mensus period is regular.i am taking tablet.from mensus 11th day 15th day i go for egg test on 15th day the size is 1.4 (left ovary) and 1.2 (rightovary).But this time 45 days finished not mensus....we tested urine today but negative came.....what i wants do to......really confused and mindly disturbed .....