20yr old.5'3 60kg.no period for 4 months.took duphaston twice a day for 7 days until 2 days back.normal pelvic ultrasound.when will i get my period?

Likely soon: If you have gone months without a period, and your ovaries have produced some estrogen during that time, then your endometrial lining will have accumulated. As long as you're not pregnant, the Progesterone medication that you took should trigger your lining to shed. It can take several (3-4) days to start bleeding after finishing the medication. If estrogen levels were too low, you won't bleed.