Talk to Gynecologist on Spotting After Periods

Dr i have a daughter and ttc for second baby since long..got fertility Treatment also. Got my hormones test u/s done also. Uptil now there isnt big issue in my reports. Monthly cycle length is normal cycles are regular. But i am unable to concieve. Had have leterozone and clomid tablet one year back. Stopped taking medicines but now issue is that -no conception -since last 6-7 months there is some spotting after periods like on day 8,9,10 etc. Dr advised to take duphaston tablet for 2-3months.its been two months i am taking this tablet. Now this month there is spotting daily,2,3spots come daily, today is my cycle day 13 i have a very tiring day and i can see brownish discharge. Please tell me ahy this spotting occurs Exactly which test are required (prolactin, fsh, lh, tsh done already, u/s done)