Sounds like depression. It could be seasonally induced, if it lasts more then a few weeks definitely consider seeing a doctor. By all means start exercising, take an aerobics class or something that forces you to be around other people in a non work setting.
You are way too young to be worried about having a girlfriend. Get a hobby and don't worry about meeting someone. Assume you will never meet someone and find ways to entertain yourself and keep yourself happy. Of course you will meet someone but why concentrate on something you can't force. It will happen when you least expect it. My friend met his future wife when she walked onto the elevator he was riding.
Would you want to date someone that wasn't happy in their own skin? It sounds cliche but waiting for someone else to make you happy never works and will crush you in the end.
If I could keep my knowledge I would trade places with you in a heartbeat.