Okay, this is the tried and true way to help settle an upset stomach from my daughter's pediatrician, and it has been successful for us:
After getting sick, don't put anything in your stomach for 20 minutes.
Start with a very small amount - a teaspoonful - of water.
If that stays down for 20 minutes, try a tablespoon.
Wait another twenty minutes, and if it stays down, increase water intake again, but VERY GRADUALLY (like 2 tablespoons). Always wait 20 minutes before introducing more.
After an hour and a half or so, if you've kept the water down, start with a small bite of a saltine cracker, along with more water.
Wait 20 minutes or so (try for 20, 15 at least), and increase the amount of saltine and water as tolerated, trying to keep as hydrated as possible.
If your stomach won't take it, go back to square one and start again. The trick is not to rush it, but to slowly reintroduce water and then food. The twenty minute wait lets the water or saltine get in your system, and then you'll know if your body will accept or reject it. Hopefully, it won't reject it!
Hope you're feeling better.
Oh, the other thing that worked once when I had to do an Off-Broadway show and had a bad case of the heaves was Lomotil, which is actually a diarrhea medication (prescription needed), but it worked immediately, thankfully. Also, Dramamine (it's over-the-counter) works because it has dimenhydrate in it, but it makes you very drowsy.
That's all from Nurse Nancy.