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Just by using Clomid (Clomifene) or Letrozole, you may not have your periods. Did you have any significant bleeding post delivery? Your weight looks fine. No periods for five years is too long, and present hormone levels will be unknown. I suggest you have any of the birth control pills of 21 twice a day for 10 days.
Throw away the 21st pill. No matter what the cause is, you will have periods within 7 to 10 days of the last medicine. On day three or four of your periods have serum FSH (follicle stimulating hormone), LH (luteinizing hormone) and AMH (anti-Mullerian hormone). This will give you an idea of follicle reserve and also if any central cause present. If both these are normal, you can start Clomid or Letrozole from day three or four and will have a much better result. I hope I have clarified your query, do write back if any more questions and for your feedback.