It is known that the bulk of the immune system resides in the bacteria in the gut. It can be restored through fecal transplants and fecal microbiota capsules. Find a healthy person and eat their feces and inject it into your anus with a bulb syringe. This is the secret to health. The animals know this, which is why dogs and many species of animals eat poo.
It's not pretty, but it will get you healthy again.