Until you have an endoscopy, don't fret. Yes, it can be GERD. What caused it? Who can say? Are you overweight? When you work out, do you weight lift? Do you eat too little protein? Do you feel like food stays in your stomach too long? Any of those can cause the condition. Your job now is to do whatever you can to help control things. First and foremost will likely be PPI therapy, which will likely help strengthen the LES. Second, if this is a symptom of another issue, like an H. Pylori infection, then that issue must be addressed. If you stay on this there's probably a good chance you can adjust your lifestyle to manage and even overcome your condition.
Belching a lot -- could be a sign of a few things, like slowed digestion, H. Pylori, or gallbladder problems. Difficulty breathing and sore throat are both signs of LPRD, which is GERD, except when the acid goes all the way up to the upper part of your throat.
Whatever it is, know that you can probably do something about it, and if you stay on it you can probably beat it.
Dont fret; if it is GERD you can learn to eat right and totally control it. I took nexium and it worked WONDERS I had GERD soooo bad and I hardly EVER have symptoms anymore!! Elevate your bed at the head a bit, dont eat or drink for a couple hours before bed, even water and that will help lots! Good luch!