Hello.
Your description of symptoms does indicate that you might be depressed. Introversion and lowered self-esteem are the consequences of depression.
You could start by taking some help from a mental health professional. There are some really good anti-depressants available today which you can take for a few weeks / months initially to get you going. Along with the medicines, you will have to imbibe some modified thinking process. At present, you seem to think about events as negative.
It is probably only your heightened anxiety about "what people will think of me" that prevents you from initiating social contacts. It's because you are seeing the world through the glasses of depression. The world is bound to appear negative, and future hopeless.
You need to modify how you take things. Do not attach values to others' opinions. What I mean by that is you are not "good" or "bad" just because people might think so.
You are going to start University. Set some really motivating goals for yourself for the coming few years. Start planning for them. And start working on them. You will realize half of your anxiety will be taken care of. You might benefit from some help from a therapist to help you modify the thoughts and beliefs as I mentioned earlier.
Wish you a very happening New Year.
Regards
This post is for the purpose of providing medical information and is not a substitute for a face-to-face consultation with a doctor. This post is not intended to give or rule out a diagnosis, create a doctor-patient relationship or replace an existing one.