Would alternating Tretinoin and AHA be helpful?

Alternating the tretinoin and glycolic acid is a perfectly good treatment regimen.  Are you trying to get rid of sun spots or just maintain a good anti-aging routine?If you are trying to fade sun spots, you may need something slightly more aggressive than tretinoin and glycolic acid.  Depending on the shade and extent of the dark spots, you may need in-office chemical peels, prescription bleaching creams, or IPL laser treatments.  If you are just trying to maintain and make sure you're on a good skin care regimen, I give you an A+!  You are way ahead of the curve so keep it up.

This is a good regimen for removing damage and at 22 you do not need any additional treatment .This will gradually remove minor discoloration as well as minor acne.

You are on a good anti-aging regimen: Skinceuticals CE Ferulic, topical green tea, Tretinoin 0.05% Cream, and ZnO sunblock. You can try alternating 10% glycolic acid cream and Tretinoin 0.05% cream at bedtime or increase to Tretinoin 0.1% cream every night and use the glycolic acid once to twice weekly. Both products help improve the appearance of your skin -lighten brown spots, help stimulate collagen, and smooth and exfoliate the skin.