Trying to unpick this.
- Previous medical assessments have not uncovered any reason why his reaction to a cold is much more severe that normal.
- He has a history from childhood of extreme reactions to ill health courtesy of his mother.
- The situation from a family perspective is untenable. He's risking his employment. The children don't/can't be around him when he is poorly and have to leave the family home. The OP has to sleep on the sofa.
I'm reluctant to simply dismiss this as "man flu". There is something else happening here. We are way beyond a person putting on the dressing gown of doom, the pj's of pity or the shuffling slippers of sorrow.
He either has an undiagnosed physical or mental health condition.
Either way, as an adult it's his responsibility (especially in light of the family impact) to get this addressed at the point he is well.
The rinse and repeat of A&E requests when he is unwell is pointless.
He needs to take responsibility for his health by visiting the GP and being candid about what is happening. Ideally if this was my DH I would want to be at the appointment to make sure the GP had all the facts (the childhood history, family impact, the results of previous medical investigations, the severity of his response).
There is no point anyone on here trying to diagnose the DH.
We tend to put a lot of faith in medicine/doctors but there are absolutely circumstances where a person's condition has been misdiagnosed or assumed to be a result of mental health issues. We have no way of knowing if that's a possibility here.
For example, buying multiple thermometers may sound odd, but if you were experiencing massive bodily heat spikes that a thermometer didn't register what would you do? It's not necessarily an irrational act.
So the only advice to give is that for me personally I'd be at the point of this being a dealbreaker unless he accepts this is not normal and gets help and is candid with the GP.
Clearly some intervention is needed, what form that takes is not.