I have had bouts of chronic coughing also. My doctor explained that there are 4 main causes of typical chronic coughing:
- post nasal drip
- acid reflux
Unfortunately, I have all four.
It sounds like you have ruled out the allergies and asthma. Have you tried treatment for acid reflux? I was tested by a GI specialist who confirmed I had acid reflux even though I had NEVER had any heartburn. Often the reflux cough is a sypmtom of LPR. Your symptoms seem like they are an exact fit. Often with LPR, the coughing is better at night. The cough after eating also fits with your symptoms. You can read up on it on the acid reflux board. There are ALOT of threads on it.
For me, taking two doses of Proton Pump Inhibitor medication has kept me cough free since mid April. That is a record for me in recent years.
Good luck in your search for a cure.