It's likely acid reflux. Seriously, when it gets that high it sometimes creates a feeling of a "lump" in the throat. (It may also create a feeling of tightness, especially when you talk, the feeling that little things like rice get stuck in your throat sometimes, and in some cases cause difficulty swallowing.)
Recommendation: stop taking vitamin C, since it's an irritant. Get your vitamin C from sources like spinach. (Avoid citrus for the time being.) Additionally, mucus will make your acid worse because it's an irritant to your digestive track. (When mucus hits your stomach it presumes it's carrying with it viruses and as such churns out acid to kill everything in there.)
I highly recommend you go see a doctor, as you might be experiencing symptoms of LPRD. (It's like GERD, but with the upper esophageal sphincter.) Additionally, if you've been experiencing a lot of acid reflux, you may want to request an upper endoscopy (EGD) in order to get a baseline of the damage that might have been going on. Left untreated, GERD and LPRD can lead to very nasty conditions. Treating it early, being careful with diet and exercising will pretty much prevent those nasty conditions. Finally, increase your protein (lean meats, preferably fish like fresh salmon and tuna). This strengthens the LES, which reduces acid reflux.
By the way, the reason you may be feeling that lump but no other sensations is because while acid is corrosive in the esophagus, the lower part of the esophagus has natural defense mechanisms which are designed to be able to take SOME damage. (Acid reflux is at times used by your body as a way to kill bacteria.) However, the upper part isn't designed for this, and so when you start getting acid all the way up there, you get damage much quicker.
Thank you so much for all the helpful information.