Find some pics of guys you would like to look like. Try to find some that look in some way similar to yourself, then try to look more like them. Get their haircut and wear those clothes. Try out some different looks to see which one you like.
If you take care of yourself with lots of good grooming and cool clothes, you will look nice.
It sounds like you may just not be having a good day. You're having what many girls call a fat/ugly day or days.
For the rest of tonight, relax, do things for yourself and do little things. lay around, watch a movie and relax. Tomorrow is when it all changes. Tomorrow is when you don't listen to the negative crap in your head. Tomorrow is when you eat better and work out on a regular basis. tomorrow is when you stop comparing yourself to other people and just become yourself.
Go to the mirror and tell yourself you are sexy. It could just be a time in your life where you do not have much confidence. It could be part of your past some trauma like a (bad break-up, new school) something like that where you have felt isolated and alienated and you associated that with being ugly. Maybe you feel as though you broke a norm of some sort . Or maybe it is happening right now. The question is why do you feel unattractive? I suggest making a list of things you think are wonderful and attractive to yourself and another of all you don't like. The best way to love yourself is by starting with the things you don't like and say, "I love this_ "
Make yourself a better person. Get in better shape physically, read something deep, write poetry, go to book readings and above all ask people you admire to spend some time explaining things you don't understand!