The same product now stings after I opened a new bottle.

Pause the product and check whether the formula changed, how it was stored, and whether anything else in your routine changed. I would treat the new reaction as new information rather than dismissing it because the product used to be fine.

A familiar product can still become a new problem

Previous tolerance does not tell us the cause of today's reaction. If symptoms persist or include swelling, get medical advice rather than keep testing it.