Where should I incorporate a vitamin C serum into my regimen? I use Aczone in the morning and Tretinoin at night.

Retin-A is not meant to be put right on the thin skin of the eyes, and certainly not daily for 4 days to start out.  There are many good eye creams that have retinol in them that can help with wrinkles without causing the issues you are having now (I'd recommend ZO's Hydrafirm).  You...

If you are trying to conceive, you should stop the use of Retin-A. It's ok if you began using it a month ago. Just discontinue use now until you're finished breastfeeding, if you choose to do so.

There are multiple layers of skin. Proper use of retinol or Vitamin A products results in thickening of the living layers of skin and thinning of the dead layers of skin. The overall result is a net thickness of your skin. It can take several weeks for the skin changes to settle down and up to...