Can you use tretinoin & glycolic acid together?

U can use it together. If there is a negative effect when the second layer. It's better to stop

You can use it together, but be cautious. If you just started tretinoin, I would advise against it until your skin is used to the tretinoin, and then slowly reintroduce your AHA's. I'm able to use 0.05% tretinoin as well as AHA's both nightly with no adverse effects. However I also do the 7skins method with all hydrating toners, and sandwich my tretinoin with moisturizer and a sleeping mask.

Nope, instead alternate nights. Limite the aha to 2-3x a week at night maximum else you will severely compromise/damage your skin barrier