Please help! We are planning to go to Cancun, and won’t need a test on arrival back to US since we tested positive within the last 90 days. Could someone please share their experience if you were in the same situation? Thank you!!!

Why not just get a test they're offering travelers in Mexico & save yourself the worry?

1) CDC doesn’t recommend testing within 90 days from positive result: higher chance of still testing positive. That’s why this exception exists for recovered individuals.
2) fear of false positive.

Airlines don't require a test before leaving Cancun if you've been positive within 90 days?

I returned from Cancun a week ago. We were tested at the resort, process was easy and quick.

Why don't you ask the airline you are planning to fly, they are the ones you most have to worry about. I guess you are worried the airline will require that test of those boarding.

these are the rules for Delta

• Customers who have recovered from COVID-19 can travel with a positive test (taken within the past 90 days before travel) and a letter from a licensed health provider or public health official stating that the customer has been cleared for travel

So for them, sounds like you have to have those docs to prove this, not you just saying this. Maybe that's not what you meant you were going to do, but I think you should ask your airline for sure.