Welcome to our little band of heathens.
I wouldn't be able to comment on your appearance or social skills. Though, you seem rather well-spoken enough.
At the risk of my words being ham-handed and void...
All I can say, from your introduction, is that you seem to think negatively of yourself. If you do, you'll communicate that to the rest of the world. It's after-school special crap, I know, but you got to respect yourself before others will respect you. You gotta become confident in that you're worthwhile, if you want others to think you're worthwhile.
From age (about) 10 to (about) 17 I was quite obese, obnoxious, convinced I was unlike anyone else, antisocial, didn't put any thought in my outerward appearance and was convinced that who I was, would never change. I was rather depressed, obsessed with my 'oh-aren't-I-so-tortured' attitude and both desperate for validation of others as well as disdainful to their opinions. It made for a needy, angry mixture that wasn't fun for anyone.
Now, I have basic respect for you. I do. And maybe my experiences don't wholly translate to yours. But why I mention them, is that it's important you need to switch your mind-set and break this negative spiral. The first step to accepting you can become better, is accepting that there are things you need to work on. (For me, this took the longest of time to accept. As I was pretty convinced I was great, despite it all.)
If you're not impressed with your own looks and physique; don't just accept it. Start exercising, diëting, following dressing and fashion shows on tv (if that's what it takes), concider mixing up your hair, ... whatever.
If you feel like you're not striking a significant impression or are feeling depressed; don't just accept it. Go take a course on assertivity. Join a self-help program. Take therapy if need be, there's no shame in it. Put out small goals like; going to new places twice a week or making a passing remark about the weather to a shopkeep.
If you feel like you're not intelligent; don't just accept it. Start reading more books. Take a class or an online course. Take a newspaper or national geographic membership. ... There are plenty of things you can do.
The important thing is that you set goals for yourself and celebrate your journey towards them. Take small steps, don't overreach. Plotting this out and staying aware of every small thing you do, every book you read, every jog you take, every soda you pass up for water, every conversation you spark, is an enormous help in changing your mindset and thus how you communicate yourself to the outside world. From toiling in helplesness, you transform yourself into your own architect. You acknowledge where you are, that takes guts, and you are the reason why it keeps improving, bit by bit. It keeps you busy. It keeps your mind off bad thoughts. And you'll find, in time, that people will treat you better. They will respect you, because you respect you.
Again, sorry if this is not helpful. But I can only advise this, reading your post. Think big, yet start small.