My son has recently had chickenpox for the third time. All 3 times confirmed by doctors. All 3 times he gets a spots that do not reach the blister stage. 1st time was around 2 years old, second time around 6 years old and again now at 10 years old. Most medical professionals either both professionally and family and friends all say they have never heard of someone having it 3 times. 2 sure but never 3. I'm wondering if I should be worried about my sons immune system at all or what it means? Additional info that may or may not be relevant :His father has Rhumatoid arthritis and I have never had the MMR vaccine.