The vomiting, nausea and feeling lightheaded, combined with the stomach pains sounds like a typical flu bug to me. It's that time of year and I don't know about you, but where I live, people are dropping like flies with it. Adding some stressful times to the mix doesn't help, but I think your doctor may have been a bit hasty to tell you it was all stress related. It's good that you are staying hydrated and you might want to try some Gatorade or other drink that will also replace some of the electrolytes you're losing from the vomiting. Do you have any fever?
I don't know what to tell you about keeping your pain meds down if your just vomiting them back up. Is the pain bearable that you could skip them for a few doses and try to let the vomiting pass? Otherwise I would advise you to talk with your doctor or a pharmacist for some advice.
Sounds like you could do with a couple days of couch time and obviously a solution to your stress.
If you're symptoms go on for more than 2-3 more days, you definitely need to see your doctor again.
Let us know how you're doing, OK?
Peace
Greenlydia