Dark Brown Spotting. Request please

Respected Doctors, Myself 27 years old and my husband 33 years old we are trying for pregnancy from 1 year. We both done with the clinical tests and everything is fine from his side but my side iwas diagnosed with pcod this month my doctor suggested letrozole after taking letrozole I was ovulated on 24th day of my periods done and today was 7th or 8th day after ovulation but I can see dark brown spotting wheather it is implantation spotting or not I don't know I'm really confused and worried if it is implantation spotting how many days it will exists ..With implantation can I get pregnant after how many days I need to take pregnancy test. I do have back pain , breast changes symptoms as of now Kindly help me out on this doctors it's my humble request please🙏