I am constantly clearing my throat

I am constantly clearing my throat. This has been going on now for almost 3 years and I'm totally frustrated now. It gets worse when I get excited. I have had all kinds of allergy testing, upper GI, Endoscopy, cat scan of sinuses, x-ray of the chest, now on medication in case it's a tick of some sort. My nuerologist does not think it is. I have Multiple Sclerosis and my doctors do not think it is associated with the disease. I have also been to and Ear, nose and throat specialist. He put me on Predisone for a couple weeks as he said I had a sinus infection. That was 3 years ago. I've been told I have acid reflux ( I have no heartburn) so I am on 2 Prilosec a day and 1 Clariton a day for that issue. I am on other meds for my MS. I have stopped eating anything with cream sauces and fried foods and it has helped, but is still there especially when I get excited. Any information anyone has will be most appreciated. Thank you all for letting me vent.

Sincerely,
BA