I think you're in for a diagnosis of IBS, OP, though I don't personally believe that's a diagnosis - more of a 'giving up and won't investigate further'.
I have a lot of your symptoms but also have the bigger problem of POTS (which you are unlikely to have based on digestive symptoms alone) and was told this is probably resulting from that. I saw countless gastro specialists over the years before my diagnosis who told me I had reflux, motility/stomach emptying issues, IBS, chronic constipation...Anyway...I have a great new specialist now so hopefully I'll finally get somewhere.
IBD (chrohn's, UC) could be at play if gluten is an issue but I don't tolerate gluten well and I don't have those so don't panic.
Have you tried anything for any of the symptoms? Buscopan/mebeverine for cramps and diarrhea? Silica? Movicol/glycerin suppositories/fybogel for the constipation? My colorectal surgeon swears by daily flaxseed but I keep forgetting there's some in the cupboard. PPIs like lanzoprazole or cimetidine/ranitadine for the acid?
I use glycerin suppositories almost every day but am about to start prucalopride for the chronic constipation (a motility activator rather than a laxative). That's after 30+ years of it though. I take a few Movicol when things get really backed up.
For reflux at night, the best thing I found was Gaviscon Advance just before bed. It was recommended by an ENT and it really helps as it puts a sort of 'float' on top of your stomach contents. PPIs don't help me. I bought one of those wedges but struggle to get comfortable enough to sleep on it.
I feel sick about 90% off my waking life but not often to the point that I vomit. There are medications that can help (domperidone/stemetil/cyclizine/ondansetron/promethezine) but they don't often like to prescribe them. Stemetil you can buy OTC for migraine-related sickness, promethezine is OTC phenergen and cyclizine can be gotten from a pharmacist, if I remember correctly. Not that I'm suggesting you take any of these - I just know how much it can impact daily life.
I chew a lot of Gaviscon dual action tablets but they only take the edge off because I have a lot of acid. Ginger capsules sometimes help me.
I hope you get sorted. It's bloody miserable.