Until you can see a physician to try to determine the cause of your problem (and hopefully, you will be able to do this especially if your symptoms become worse or more extensive)---I would advise that you go with your first inclination and avoid foods containing MSG. Reactions to MSG are becoming more common, probably because people are considering the fact that MSG may be the cause. It used to be known as "chinese food syndrome". Here is a link to an article on the MayoClinic.com website about Monosodium Glutamate.
Your problem will be avoiding the additive, because labeling does not always say MSG or monosodium glutamate (though this is changing gradually). It may be listed as "flavor enhancers", or "natural flavoring", and a couple of other terms. So, for now, try avoiding anything that comes in a can, bottle, or package. You can make your own gravies, sauces and salad dressings. And at restaurants, ask for no dressing or oil and vinegar that you put on yourself. The restaurant employee may have told you that there was no MSG in the dressing, but chances are s/he did not read the label, or did not recognize the terms used on the label.
It would also help you to do an internet search for monosodium glutamate to familiarize yourself with other terms used on labeling. Then be diligent in reading labels of anything you are going to eat.
If your symptoms continue on a diet of only unflavored plain food items, then you can start thinking about seeing a doctor to get your problem diagnosed.