I have to be honest, I'm struggling a bit to move past my initial reaction of "how utterly pathetic [of him]" which I feel guilty about because I have a couple of so-called invisible illnesses, but they do make me a little impatient with apparent health-drama queens.
Like so many others, his childhood and possible neurodivergence jumped out at me. In fact, they each crossed my mind before I got to the bit where you mentioned them. And if the latter then sensory issues may well mean the discomfort he experiences is very real.
Regardless of whether there is legitimately something physical going on - neurologically or not - he needs to learn coping & management techniques ASAP. Therapy will help with this.
As an adult who grew up with intensely painful conditions, I expect other adults to adopt coping strategies. It's one thing to suffer, it's another not to take any responsibility for living with it.
However, as others have pointed out, you both need to be sure there's nothing else going on which can be treated.
I wonder how much is a physiological stress response. He's not alone in coming down with something every holiday or catching everything the children have. Men at work almost invariably become constantly ill when they have infants and most people who work full time end up with gasping immune systems come holiday time.
So, in addition to the above, get him doing some mediation or breathwork daily. Just 5 minutes - or even 3x a week and build up. General health improvements - exercise, diet, fresh air and quality sleep. Vitamins. Check for deficiencies and take a good multi vitamin. This will all help his immunity and make him less vulnerable to pain.
Oh and if nothing else, get him to download Curable. It's brilliant for chronic pain suffers and genuinely makes a big difference,I think it could really help him.