I would suggest keeping a diary of everything that's going on BUT keep it as brief as possible, get a good hardbacked notebook for the purpose and note:
Diet (inc amounts)
Medication (type and dose but ALSO record if taken late/forgotten - not ideal practice but can lead to discoveries and let you know if effective or not)
Habits - smoking and alcohol consumption are main things I'm thinking about - not always a negative thing, sometimes smoking or a small amount of alcohol can help some things and if so its worth noting as it can give clues eg alcohol can alleviate some forms of angina, smoking can help certain bowel conditions - not recommending them for these! But recording such partaking could give a clue to what's going on.
Activity (inc any injuries or strains noted) -
Environmental - could be a trigger to his symptoms, you'd be surprised. I have allergies to some really bizarre things that can be really hard to avoid. Or has your new home been checked for pollutants, toxins or allergens? Have you a working CO detector? Is it an old house? Radon is something we had to have one home checked for, there's also moulds, fungi etc I had been asthma free for several years and then moved to a house next to a rapeseed field - that summer asthma back with a vengeance!
OR certain environments may be causing improvement and THAT can be a clue, eg many of us feel better after a day at the seaside and it's not purely down to a pleasant trip, but being away from pollutants etc if he feels better at home than when out and about maybe.
"Output" - urine - colour and frequency, faecal nature and frequency (easy enough to look up a stool chart)
Energy levels (I'd recommend a score out of say 10)
Symptoms - briefly but accurately recorded. If there are any physically visible indicators - skin colour, hair loss, change in hair colour, oedema you could record these photographically, even take a daily pic if something like hair loss occurring.
Even just for a month can help you see any patterns, minor symptoms or possible causalities. But also cos just sometimes something really daft but obvious is being missed!
Not saying this applies to you or dh (this level of daftness) but I well remember caring for a diabetic who was struggling to manage their condition, they were supposedly keeping a food diary and were indeed noting all their meals, snacks and drinks...at mealtimes - they were neglecting to include the "healthy" orange juice they were downing a litre of a day!
Also had a patient who neglected to tell us of her triple dosing herself with multivitamins - she figured they're healthy and she was feeling rotten so more must be even better right? But certain vitamins are actually toxic in large quantities and she was VERY lucky she didn't do more harm.
People can sometimes do daft things without realising - I've done it myself! Not twigging a product has changed to "new improved formula" and getting an eczema flare up, I'm also a bugger for not drinking enough and ending up with dehydration headaches - we all lapse sometimes.
"We only moved about 1/2 mile"
You'd be surprised! Even a one street change can mean a different water supplier, and the house IS different.
A feeling of impending doom CAN be a symptom of some conditions so include in the diary - epilepsy is one that springs to mind and it doesn't always present "typically" either but can present rarely as muscle/nerve pain.
I really hope you get to the bottom of this soon.