Why I'm so anxious. What should i do?

Start step by step to make discipline schedule of your waking and sleep time. Instead of going and mingling with all first be with those with whom your more comfortable and then you start having conversations with new people too for this you can take counselling too. As you said you overthink and keep thinking about your behaviour first understand what you will feed your mind it will go in that way you try for cognitive behaviour therapy this helps to change your cognitive thoughts and change your behaviour to look and act towards certain situations. As you mentioned you don’t like to be alone but feel drained when you go out. Usually happens when we don’t enjoy the actual company of people we have but force ourself to be there so try to hang out with people whose company you like. Start some new activities to learn, pick up something new play games or classes you would like to learn people with similar Interest. Go step by step for any help do consult.