Suggest Treatment For Infertility

hi m 26 yrs old. 2 yrs before i had normal menses lasting for 4-5 days. but then i started having periods for 1 day only and that is also very little flow.
my ultrasound report is normal. then what is the prob.? i m trying to conceive for last 1 yr. my gyne says i m not ovulating and i was on letrozole for 3 months but failed to conceive . this time she recommended siphene. i want to know how could i bring my cycle back to normal ?