While it does probably feel 'out of the blue', your body probably has been struggling with these sensitivities for a very long time. Were there any triggers like life changing things (new job, wedding or divorce, a death, taking antibiotics for a long time)? That is often how it goes when someone feels like this happens out of the blue. Their body struggles but manages and then sometime in 30's and 40's (sometimes later)--- something happens and the body says "nope" no more.
Unfortunately, since you see the cause, I think you do have to alter some things. Caffeine is an easy one. Begin weaning off. I like it too but you can live with out it. It is usually in pop which is empty calories or coffee which you can learn to like without caffeine. It take 2 to 3 weeks to be over the effects of getting rid of caffeine. Big pain, I know, but it is what it is.
Limiting salt has gotten easier. Cutting back on sugar, you can do that.
I know you aren't liking my remedy but it is what it is. I hope you are able to make these adjustments.
I agree with specialmom that it's probably not a sudden as you might think; your body may have been struggling with this for a while and you simply didn't realize it until it became a problem.
Why not try an elimination type of diet and see if it's all of these foods or just one/some of them? You could try eliminating all of them for a couple of weeks, then try adding them back in, one at a time, except sugar - that's one that should be eliminated for good.
Perhaps it's not "all" dairy that upsets your stomach... for instance, some people can't tolerate lactose, but they can drink lactose free milk. Personally, I eat some types of cheese, but rarely drink/use milk because milk causes me to feel bloated, cheese doesn't, nor do I eat yogurt, but I can eat a bit of sour cream.
Caffeine is found is many different things - sodas, coffee, tea, chocolate so one really has to be diligent when trying to give that up. I've gone to half-caffeinated coffee and that's helped considerably, but some people can't do any caffeine. I don't drink soda at all and I'm not a chocolate eater.
One thing that we tend to forget is that many/most things that contain caffeine and/or dairy also contain, both sugar and salt so we're constantly exposed to those. Look at the chocolate bar, the cookie, the processed meal, the peanut butter, the carton of fruit flavored yogurt, the ice cream... almost anything we eat, unless we make it ourselves from scratch, has sugar and/or salt in it.
It's not easy to do an elimination diet or to eliminate any foods from our diet, but when they cause us distress, we really have no choice and it can be done with just a little planning. There are all types of coolers and containers in which we can carry food that we prepare at home or carry fresh food, so we can eat more healthy. Shopping and prepping food on days off makes it easier to toss something into the cooler to take with you.
Hello~I have heard that a persons' allergies or sensitivities can change every 5 years, so maybe your system has just become allergic to these foods. Try to stop these offending foods all together for a while and then starting adding them again, one by one in smaller amounts, this might help to "re-adjust" your system back to where you can handle them again.