I'm so sorry to hear that you ar suffering. Given the fact that your endoscopy was four years ago, you may want to request a new round of imaging tests. With your symptoms, it could be SO many things. If it was a meal or a series of minor causes, you wouldn't be posting here, still looking for answers. Keep an eye out for fever. If it comes back along with either/or vomiting or pain, that's a great indication that you might want to go to the hospital.
Here are a couple of things that I've found helpful.
Research! Read old posts in this forum. There is a fantastic research resource that I've found very helpful called "The First Principles of Gastroenterology": http://gastroresource.com/GITextbook/en/Default.htm. For nausea, visit: http://www.medicinenet.com/nausea_and_vomiting/article.htm or http://www.mayoclinic.com/health/nausea/DG00019. This article has a chart with possible causes of abdominal pain: http://www.emedicine.com/med/topic2740.htm.
Log! Keep a journal. It helps identify patterns in your symptoms, foods, medications, temperature and pain level. You're welcome to read mine but I write a lot (can you tell?). :)
http://www.medhelp.org/user_journals/show/12546?personal_page_id=8912
Reach Out! You are not alone! Try to stay positive.
When you do find answers,please post to let everyone know what you found and how you got rid of your symptoms. It gives people on this site hope to hear success stories.
All the best,
Sam