Skin barrier repeatedly getting stripped when I use actives or is it my Vitamin C serum?

Hi! I had a great skincare routine (I am 50 F) with a cleanser, serum, moisturizer, and AM sunscreen. PM, similar but no sunscreen, and would use an active ingredient, rotating among prescription retin-a, vitamin C, or niacinamide. I stripped my skin's barrier a couple of months ago. I thought it was from having too many actives and just overdoing it (but it was odd, as nothing I was using was new — ingredient-wise — and I really don't think I went overboard). The only culprit I can think of is a different Vitamin C I got (Remedy brand), because last week I added it back in just once (I had calmed my skin down by using only Cetaphil cleanser and moisturizer), and it happened again. So it seems obvious that the Vit C serum was the reason, but now I'm still scared to add in actives. Why is my skin so sensitive now, and what products for texture and dryness can I add in without fear of this happening again? Or maybe it was just this one product? (I threw the Remedy Vit C away!)