I am going to do ivf. I have starded decapeptil injection from 21 day after period. But this cycle haven, t started yet. (4 day delay)what to do?

Ultrasound & bld wrk. Decapeptyl may have thinned the lining very much that no menstrual blood came out. If ultrasound does not show a cyst or advenced follicle and your estrogen and fsh are low you can start your ivf cycle.
Speak to your doctor. When doing ivf things can vary from person to person but it is very important that you communicate well with your doctor. Nothing to worry about. Often it is delayed a week or so.