A sore throat
in the morning is usually a symptom of some sort of irritation that is occurring during the night. There are two or three very common reasons for the back of your throat to be irritated. While you don't mention how long you have been having this sore throat for, it is possible that you recently had a very mild upper respiratory tract infection. The extra mucous that this causes your nose to make has a tendency to drip back onto the back of your throat when you sleep at night. This is very irritation to the gentle tissue, and can cause inflammation and dryness that improve with moisturizing over the course of the day.
Another reason that a simple cold can affect you like this is by causing you to breath through your mouth (especially at night) because your nose is stuffed. This obviously will dry out your throat as well. A second common cause of a sore throat in the morning is acid reflux
, or gerd. Even though you are still young, going to bed with a full stomach can be enough to cause your stomach contents to overwhelm the valve that separates your esophagus from your stomach. This leakage of acid can burn your throat. You should speak to your primary care doctor
if these symptoms continue or you have other symptoms.