Ovulation/AF after an ectopic.

Gouri
Does any one know how long for  ovulation/AF cycle to start after an ectopic. I had an ectopic pregnancy removed 3 weeks ago. After a week my hcg fell to 39 from 900 and last Monday it went down from 39 to 7. How soon does ovulation happens? My obgyn has advised to wait for 3 cycles before we try. Just curious how long until my first.