Thoughts of a non-medical-professional person and not meant to be medical advice, but things I've encountered and done:
Stress - Yes, stress can do that to you. I went through that on and off for years when I was in a stressful situation. At one point I remember having a plate on my stomach/midsection while I was laying down and everyone in the room could see my heartbeat by how much the plate was moving. Until you take care of the stress - good stress, bad stress, it's still stress - it can play havoc with your body. You've had a major upheaval in your life recently. While it's a good thing, it's still stress!
Probiotics - a lot of them are destroyed by stomach acid, and don't even get to your gut. So if you go that route you'll want to find something that's coated and will actually make it to where it needs to be. Apparently having them in a dairy food can help buffer the effect of the acid, too. The Placebo Effect is well documented with some people who improve suddenly who are popping non-coated pills.
Bugs - you may have picked up a bacteria you're not used to, and have a case of gastritis. Sometimes that can take quite a while to settle down.
Other things - Could be IBS. Could be GERD. Could have something to do with your gallbladder or bile ducts. God forbid, it could be the start of ulcers. There's a lot of exotic and less exotic things that could be going on. And very little way to know what they are without some testing - and even then you might not know!
Food Sensitivity - Could be a food intolerance or sensitivity you've developed. For example, there are proteins in cow's milk that some people are allergic to, but they can drink milk from cows that have a slightly different protein - I think it's Type A1 v Type A2. Perhaps the dairy cows here are different from what you're used to (or they're fed something different) and you're just now running into the problem? If you have milk products at every meal... then again, if it happens when you've not had dairy, that particular example would be ruled out. They use a lot of beet sugar here rather than cane sugar or corn sugar as in the States. Sugar is sugar, chemically, but there may be some hitchhiking molecules.... My point is, if it's a prepared food, it could be almost anything in it.
The EU has stricter regulations about keeping a lot of the nastier stuff that you still find in processed food in the States out of the food here, but there's still a lot of "stuff" in processed food. So, it could well be that there's something here - maybe a sugar substitute (one of the sugar alcohols) that's causing you trouble. (I personally have hell with those.)
Maybe, try: In the past, what I'd do in these situations is go on the BRAT diet for a while to see if I could weed some obvious things out. Bananas, Rice, Applesauce, and plain toast is the BRAT. I have, a few times, dropped it down to just the white rice and chicken broth for a couple of days, then added the other things in over time, one at a time. It's hard to live on that if you're working and away from home, though, so the whole BRAT might be more sustaining. Drinking nothing but water or maybe a clear broth is good. I'd do it for a few days to see if things settle down with the tummy. If it did, I'd then slowly add more foods into my diet, no more than one a day. Absolutely no alcohol or caffeinated drinks until it sorts out. Probably no fizzy drinks, too. I'd not go for a lot of hours without something in my stomach - dry toast, rice, crackers, something. With a strategy like this, as you add more foods in, if you're sensitive to something hopefully you'd get a pretty quick reaction and could then know (or check the ingredient list for possible suspects) what your body doesn't like. If you don't feel better after a few days on the really restricted diet, or if it got worse, I would assume it's not food-related. (Unless the culprit is Bananas, Rice, Applesauce, or something in the bread.)
Time - Sometimes I found that my stomach had gotten irritated for unknown reasons and just giving it a bit of a rest was enough to reset things and heal up. If you had a new virus or a new bacteria introduced to your system, it may take a while for things to balance back out again. Sometimes waiting is all you can do. But I would add that absolutely if you are in pain or it's getting worse rather than better, see a medical professional sooner rather than waiting. If you can do a bullet-point list of your symptoms and how long each has been going on, it might be useful to bring along.
Best of luck - I hope you feel better soon!
PS - Worrying about it is not good, though. Adds to stress! So don't let it go on too long.
