I'd try and see an immunologist as soon as you possibly can. If it reacts going out in the sun, that could be solar urticaria? Often urticaria's come in clusters, I have cold, spontaneous, stress-related, allergy-induced and rarely delayed pressure. The painful joints and back and swollen fingers could be angiodema, but it could be rheumatoid arthritis. Immunosuppresants can help with all of that.
It is hard with partners, family and friends. People don't tend to understand how bad this is. There is a research paper on the psychological / emotional effects of urticaria. Maybe try to find it, and have him read it. It explains that urticaria makes a person suffer as much as as serious heart condition or cancer. Getting into the care of a specialist in Urticaria will help with that. They can also prescribe things like immunosuppresants, which are much better to be on than steroids. You could ask to be put on Dapsone first, as that is milder and works well for some people. They'll need to run blood tests with those.
Yes, don't take any OTC painkillers especially Ibuprofen, that drives my skin wild. Gabapentin can help with bodily pain, itching and sleep and help reduce anxiety / depression. that. So can beta-blockers. So can tricyclic anti-depressants, and can help with depression, but has much more drowsy side effects. SSRIs can be sometimes be helpful too. It's important not to let anxiety and depression set in too much. Stopping it earlier is better.
I'd ignore your partners reactions and go easy on yourself. Just take it easy, forget about work, money and what people think. Get more sleep, eat very very healthily (mostly vegetables) and take up hobbies that reduce stress that you enjoy. You know you are very ill, and many people here have been through it. It is very bad, especially before you find treatment that works. But I promise, it does get better if you just accept that you are very ill and don't beat yourself up or let anyone else tell you how you should cope.
You could do worse than go on a paleo diet and kick common allergens, gluten, milk etc...
Meditation, yoga, tai chi etc... will help you with the stress. Do try to get outside to walk, it will help with depression and anxiety and join pain, but use a broad hat and cover your skin. If it's solar urticaria, it won't react if your skin is covered. Sometimes, you can have cold urticaria and it will be the wind, not the sun. Do a test with an ice cube on your arm. You can do a similar test with the sun on just a patch exposed on the lower side of your lower arm. See if hives or itching starts where it is exposed to cold or sun.
Work is tough, I had to give up working for other people for a while. But now I work for myself, control my own timetable and can take time off when I am struggling. When you are better, you can have a think about what could suit you for work. But don't worry about it for now. Sometimes the stress of life and especially work can be one of the causes of this. But for many people urticaria runs it's course after a couple of years. I know that's a long time, but it isn't a lifetime's curse for most people. But do get checked out for rheumatoid arthritis as that can be treated, but does harm if it isn't.