Don't feel like you are going nuts. It seems like a lot of your symptoms are new to you and we all want to know what is going on with our bodies. There is definitely nothing wrong with that and only we know when something doesn't feel right. Don't make the doctors make you feel bad, unless your lucky to get a really good doc, most of them make you feel like you have a number on your head and want to get you out of the door because you are taking from their profits. (Sorry, but thats how I feel) When in doubt, get a second or third opinion.
Having both IBS and GERD myself, I can relate to a lot of your symptoms. The problem with IBS is that it is only officially dx'd when all other problems can be ruled out so even though there is not something that they can see, it doesn't mean that its not there. :) I'm sure the ENT specialist wasn't looking for GERD and just because he looked down your throat doesn't mean anything. The esophagus is located below the throat and it can't been seen without a CT or xray. Most doctors will dx GERD from a series of questions, ie. how many times do you burp? how many times a week do you get heartburn? what are your coughing patterns? and so on.
IBS, Diverticulosis, GERD, Cervical Disc Degeneration
"If you don't like something change it; if you can't change it, change the way you think about it" - Mary Engelbreit