TTC- Why is it taking so long?

Sarah

Had the dreaded period turn up today. Cycle 11. Absolutely gutted finding it really hard. Already have an 18 month old that I got pregnant with first month trying but my periods were very regular bang on 27 days. But my periods are anything from 26 to 33 now. I've tried opk tests but found then difficult to read. I had a c section then sepsis when I had my daughter and been on sertline and worrie if either of then will be making a difference. Just wondering if anyone had any advice or help. Please and thank you.