There is just sooooo much in your post that I can relate to & counselling both for me & the DH & I together has helped massively.
DH can be similar over money, though DD & I just take the piss out of him when he starts, so he soon gives up. He also lost his mum, we've lost friends & have been through very difficult times with DD who has disabilities. I also have chronic health issues.
Is your DH a worse Scrooge now since losing his DM?
What we've realised from our situation & counselling, is that DHs money issues stem from childhood. I didn't get that as his DSIs is very different. Turns out there was abuse around him asking for treats, such as looking at a cake longingly in a shop & saying he'd love that & then getting smacked very hard for it. But never his Dsis. That sort of thing.
His DMs death hit him hard, but he bottled it up too. We are all guilty of that though as we've had a lot of close deaths in the last few years. This brought his childhood trauma to the fore & he also became ridiculous over money wasting... I was close to him wearing mouldy beans that I'd put out for the bin several times.
& 2 teens, jeeze, 1 has all but destroyed me this last few years. & I'm learning that they ALL complain about how tight we parents are & how much more their friends get at that sort of age. Ours has only just grown out of that at 18, when we pointed out she was now an adult & a CF, so she could work if she wanted money. In fairness she's now got herself 2 jobs & is saving hard for Uni
I'd suggest counselling for yourself. It helped me recognise just how much we have been through & are dealing with still & it helped me to see that we all needed to cut ourselves some slack. Counselling together if yours is open to it would also be a good idea.
Mine was reluctant, moaned like hell about the cost ofc, until I looked him in the eye & told him that divorce was going to cost a fuck of a lot more, so he'd better get his priorities right. In fairness he's been great since then & is taking things on board & things have hugely improved.
The huge stress you are under is going to affect your health, so you really would benefit from counselling support. It's really helped me get back on track health wise
As for your health issues, some ideas based on my experience...
My IBS turned out to be twofold. (DD indirectly too) I had Heliobacter pylori infection that was never checked for in decades, despite all of the tests you described. Make your GP check you thoroughly for that & read up on it & testing. This made a huge difference to what turned out to be largely gastritis caused by h.pylori for me
Make them check you for B12 deficiency. Also folate & iron. That causes all sorts of problems, including worsened allergies & so sinus trouble. It can also make you food & additives sensitive & cause allergies that affect the gut. DD & I both turned out to have this & she became allergic to soy, which is in lots of things. It caused her to have allergic colitis, which was misdiagnosed as IBS for years. Her B12 injections with cofactors vitamins cured her allergies & massively improved her chemical intolerances. Google Tracy Witty B12 for a great reliable website
Your GP can do an Immunoglobulin E test (IgE) this shows whether or not you have a true allergy. If for any reason they can't. They need to refer you to your gastroenterologist. It was a Gastro Dr that did this for DD. From there you can work out what you're allergic to with exclusion diets. They usually look at wheat, diary, eggs first. Cutting out the culprit food stops the IBS like colitis. DD can now eat soy again though thanks to her B12
Could you be hypermobile at all? (Beighton Score Chart in Google images with help if you don't know)
DD & I both also turned out to have Hypermobile Ehlers Danlos, which is a collagen defect that makes us a bit stretchier, everywhere from joints, to guts can be affected. DD was hospitalised with what they at first insisted was IBS, but was actually an intestinal blockage due to stretchy guts caused by hEDS.,. Her ongoing diarrhoea & cramping that was blamed on IBS was actually her bodies way or trying to get faeces past this blockage. She also had a bad colitis flare up meaning Labour like severe pain with the blockage too.
The 2 together can be nasty, I've had similar issues too & fobbed off for years as IBS, but actually H.pylori, pernicious anaemia & IBS
A natural, whole foods, low wheat, low diary, no meat & no additives, definitely no artificial sweeteners etc, type diet, with turmeric as a supplement or drink "golden milk" & hibiscus tea & b12 injections helped us both a lot. Initially before diagnosis I found cats claw herb really helpful with actual IBS/possible leaky gut too