Thank you for your query.
Any kind of childbirth predisposes to backache because of multiple reasons
1. Calcium and vitamin D deficiency incurred during pregnancy
2. Laxity of ligaments during pregnancy
3. Further stretching, nerve compression during labour.
Also, since you have PCOS, that condition is inherently linked to calcium and Vitamin D deficiency.
The backache is in no way related to your ovulation / fertility status.
Please have your calcium and vitamin D levels checked, and take adequate supplementation.
Acne and irregular periods
are enough to diagnose PCOS, alongwith certain hormonal blood tests.
You might require Clomid, if your follicular studies show anovulation
You are right in consult an Infertility
Also, I hope thorough evaluation of the cause of the first stillbirth was done - postmortem examination of the baby and placenta, glucose tolerance test
, thyroid profile, liver and kidney function tests etc.