Hello~It truly does sound like food allergies to me, that, combined with the GERD would be a possibility of why you are having these issues. Another possible reason is you might have a Hiatal Hernia, this is when part of the stomach pushes up through the diaphragm muscle. A hiatal hernia can also cause the GERD and when you laugh or do anything strenuous, it can push the tummy more into the diaphragm. I would certainly ask you doctor about his.
I would try drinking very warm water, and as you swallow, give a good bounce, this might help to move the hernia back to were it belongs.
Is this a wet sounding cough? Having Gerd greatly increases your risk of aspirated pneumonia when eating. I'm not sure you'd have that chronically though as you describe. In gereral though, cough after eating does happen with acid reflux and GERD. Do you h ave difficulty swallowing? Dysphagia is another reason people may have a cough after eating. And yes, food allergies as well. I'd personally begin a food journal and take notes on what you are eating, when and all about the cough and then look for any pattern. Try adding in and eliminating foods. A small sip of water with your meals may help as well. I'm sure this is frustrating. How long has it been happening, by the way?