Infertility. What does it mean?

Hi ! We are three years married couple and from 1st year we are trying to get pregnant I am pcos and facing infertility , my Hus report is normal ! The issue is I am under medication of follic acid,vit C and bio av coq contiuesly I am taking this and last month I got my periods very dark brown colour and a small quantity just for two days it last ! So doc said me to take a pregnancy test if you didn't get your periods normally and I undergo the test it become negative so she advices me to have letroz from day 2 and surema on every morning and night ! For this cycle my tablets have been changed and I got my periods before on date it's exactly 13 days before the expected date ! Why is it my body reacting this weird ! Though I got my periods regularly every month ! And I am getting periods early this month ! What does it mean ??