Antibodies to any disease fade with time. What you want is memory of the virus in your immune system. Here is a test cleared by the FDA:
There are several labs here in the ‘hood where I live that can perform this test. If you are in a more civilized area I am sure you can find a lab close by.
They don’t fade THAT fast. I never got the chickenpox again 30 years later when my kids did!