Welcome to the GERD forum at Healing Well! You're DEFINITELY in the right place. The things you're describing are classic reflux sumptoms. An ENT scoping your vocal chords can make a very good diagnosis, as the reflux you're experiencing creates inflammation that is easy to see.
The symptoms you describe--burping, food getting stuck, gurgling stomach, excessive mucous production, the feeling of a lump in your lower throat--are all things that are associated strongly with GERD.
The Nexium you're on will take 2 weeks to become fully effective. Your symptoms indicate that you're further along in your reflux issues than you might think. Your underweight condition isn't the cause...being overweight is the issue, as things the fat causes things to push up and puts pressure on the stomach, thus creating a situation where reflux is more likely.
It seems to me that whether or not you feel your symptoms relieved by the Nexium, it would be a good idea to get a referral to a good GI Doc, so he/she can listen to what's been bothering you and try to get to the bottom of your problem.
I'm so glad you've joined our group! I'm sure others will be by to weigh in on your issues, and try to help.
Best wishes in finding answers and relief quickly!