I totally know how you feel. My highschool years were basically a waste because I was struggling to just get through each day with depression and a growing social anxiety problem and body image issues. I kept telling myself, what if I didn't become so fat and ugly? I probably wouldn't have struggled to socialise, had way more confidence, more friends and be further in life with the things I wanted to do.
But I can't change that. I am learning more to just live in the moment, took me something like 2 years to get over the anger and regret I felt over highschool and how I felt it was a total waste of my time and having no good memories of it, and all the anger I have over my parents as well and the voilence I had to witness on a weekly basis. I als had so much regret about overeating and getting fat it consumed me for a long time.
Seeing a psychologist and taking anti-depressants have helped heaps with my problems. I was so anxious the first day seeing her I was shaking, but gradually the anxiety lessened. I feel the only way to get over SA..is to keep putting yourself into those uncomfortable social situations no matter how much you hate it. I still hate it right now, but I have to get used to it. I just remind myself not to be so hard on myself if the people I talk to don't seem interested in me and I don't start a winning conversation.
My suggestion, is it just focus on the now and try to stop dwelling on the past and the "what ifs" because all it does it makes you feel worse, its not
productive and you can't change it. Took me so long to get over all the regret..just don't be hard on yourself OK. Focus on the things that you love and don't ponder the future to much either. I know its not easy, but just remember to pat yourself on the back for little changes you make in your life. Before opening up about my SA, depression and other problems and seeking help, it was almost impossible for me to get out of the house, let alone get up in the morning half the time. I spent 10-13 hours a day playing computer games to escape from everthing around me. I couldn't concerntrate anymore, couldn't remember anything, I even forgot the names of some people I knew for a long time! It was just crazy. I would always worry about any social situations I would have to face and have so much dread. I hated life so much. I was feeling suicidal and knew I wouldn't last long.
Today I'm working now, socialising a little more and trying to get back to school. I still feel hopeless and depressed, but I know I've come a long way. I can't look people in the eye properly let and find it so difficult to hold a decent conversation, but I try to work through it.
Anyway I really hope that helps.