is complex. There is a PCOS board I'd suggest you visit.

Acne from PCOS is typically due to imbalance of hormones and androgen.
http://forums.obgyn.net/pcos/
The forum there is a little hard to navigate, but there are many responses there that discuss the various treatment interventions.

I had PCOS, and it affected my ability to have children. I managed one
pregnancy, and this was before PCOS was understood. I never had acne from it, but I did have other problems.
PCOS is a somewhat beyond this board. There are many other good sites on
the net if you google it.

I think you need a good endocrinologist (hormone specialist) with the complex effects that Prednisone caused for you.

Flax oil, and evening primrose may help with the acne. Low EFA status is typically common in acne. Low Folic acid and zinc as well.
I would caution you against retinol drugs as treatment. They work on the acne but disrupt your EFA metabolism terribly. The tradeoff is worse than with Prednisone. Triglycerides go dangerously high, and the brain is depleted of DHA which is a vital EFA, and depression results. Accutane in USA it is called and has been under scrutiny for years here. It is a very dangerous drug IMO.
This is a list of side effects possible for Accutane (retinol)
It can cause Guillain-Barre syndrome and neuropathy:
http://www.bmj.com/cgi/content/full/328/7455/1537

This drug affects fat metabolism, and destroys nerve sheaths esp in the eye, but also elsewhere in the brain.
I'd stay away from it, as you already have nerve problems.