Reglin, I think, makes your stomach empty out--which is good if you get something in there that just sits there and won't go out and makes you sick. Fenergin is usually the drug of choice when it comes to nausea. I've been sick enough to take both.
Given that this came about because of a previous illness of the G.I. tract, you may want to take probiotics. Probioitcs are good bacteria that live in your intestines. When you have certain illnesses or infections or when you take an antibioitic, these good bacteria can get killed off and the bad bacteria has room to multpliy and grow and that will throw off your intestinal balance and cause nausea and especially diarrhea. I noticed that you're from the British Isles or Australia ("mum"), so I don't know what all is available to you over there or if what we're used to using here in the U.S. goes by a different name there, but you have some options. One, go to your chemist and ask him or her for probiotics. If they are lacking, then go to a health food store or vitamin store; they're sure to have them. At the very least you ought to be able to find acidophilllus capsules, although if you can find something like Digestive Advantage or Culturelle which have multiple strains of bacteria (acidophillus is just one strain), they'd probably help you more. At a minumu, eat some yogurt, unless you have a milk allergy (shouldn't bother you if you are lactose intolerant).
The thing about probiotics is that they can sometimes give you gas cramps, so whatever you chose, just take one pill or one yogurt container a day. If you have gas cramps, keep to it; they should go away in a week or so. If you're okay with the light dose after a week or two, then up the dosage. As fas as any of us here are aware, you can't overdose on probioitcs; if there's not room in your intestines for them, they flush out of your system without causing any problems. You need to be taking the recommended dosage (or even a little more if you notice they help you) for at least a month to get the full effect and to hopefully clear out all the nasties once-and-for-all. If you're normal again after a month, then you can stop taking the probiotics, although you may want to take some every now and again just as a bit of a preventative, especially if you travel out of the country or the stomach bug is going around school/town. You'll also want to take a large dose if you are on atnibioitcs for any reason so you can replinish the good bacteria that the medicine kills off along with the bad bacteria.
Some of the symptoms that you describe do concern me; namely the inability to lay down flat on your back without getting sick, being up sick in the wee hours of the morning, and spontaneous nausea. These are some of the exact same symptoms I had when my gall bladder was bad. I'm going to bump up my post on the symptoms of gall bladder disease; you should read through it and see if anything else sounds familiar. The first problem you had may not have been gastro. at all, but a gall bladder attack. Or the two may be completely unrelated. But, either way, try the probiotics. If your gall bladder is causing the problem, the probiotics won't help, but they won't hurt anything either. Better that you have an intestinal imbalance that the probioitcs will cure than to have a bad gall bladder. There's nothing to do for that but take it out.
And be aware that even if you don't have all of the symptoms of a bad gall bladder right now that I had, you may develop them later; many of my symptoms developed over the course of 5 years. It can be very hard to tell GB from IBS, but IBS generally doesn't make you nauseated--at least not a lot--and you rarely vomit with it, but vomiting is common with GB. Also bright yellow, burning diarrhea or vomit is more in line with GB, although some IBSers can also have bile diarrhea. And IBS does not often make people wake up during the night (although it does a few people). And you may have doctors tell you that you're too young to have a bad gall bladder. Well, I was 18 when mine started acting up, so that's not much of an age difference; it can get you anytime, even if it isn't as common in younger people.
Don't let anyone tell you that it's in your head. There are a lot of us out here who have constant gut problems. My doctors thought I was a bit off at first too--they said I had IBS or that they didn't even know what was wrong with me--until the gall bladder showed up bad on a test. Ha-Ha! I DID have a reason for being sick. See? SEE?!?! I wasn't crazy the whole time! And whatever is causing you to be sick is real too, even if they can't find it on a test; diarrhea and waking up from sleep nauseated is not in your mind. I'm an advocate of dragging doubting Thomases into the bathroom after a particularly nasty bout of diarrhea and pointing it out to them and asking them how come what's in your head is now in the toilet? Lol.