I have most of your symptoms (except frequent BMs, allergies, and elevated cholesterol), and I'm only 22. I feel your pain :(
I lost a lot of hair as well and I'm always freezing (classic signs of hypothyroidism). As for your high heartrate, do you have anxiety? Or maybe your blood pressure is low, and your heart compensates for that by beating faster?
You most likely have hypothyroidism, despite showing up as "normal" (this could be due to a lot of reasons, the main one being that many doctors do not keep up to date with current information about thyroid disorders and use outdated reference ranges). Hypothyroidism tends to lead to an overgrowth in Candida because your body temperature is low and the immune system does not keep it under check as well as it would if you were not hypothyroid.