Hi. Couple of things. 5.0 pH is pretty low, but was that a one-time test? in the middle of the day? Most accurate way to test urine is first thing in the morning. Do it several mornings in a row to avoid a fluke. If you want to monitor this, pHydrion paper is pretty cheap to buy.
When my pH is very low, I do feel something throughout my body though I wouldn't call it a burning. More like a "sourness" and a tightness, especially in the muscles, and joints don't work as well.
Also, sounds like you need to drink more water. More minerals, more water, more electrolytes. There's a good electrolyte mix recipe floating around here on CZ. Magnesium would probably help w/ the constipation.
That white stuff oozing up from your throat sounds suspicious. Ever had an upper endoscope done?