From experience, and bear in mind I am a blunt person, the simple truth is that people are shallow.
Unless you are blessed with making people crack up left right and centre from your sense of humor, they will judge you on looks alone. Online you will get judged on looks alone completely: On POF etc they will delete your message without reading it.
Now the way to win at this is to do exercise, and diet properly.
I am sorry if that hurts you, but I am in the same position. What I have learnt though, is that people North of just below Birmingham are a lot more polite and less judgemental than people in the South. Especially Plymouth and Truro... you seem to get physically pushed out of the way if you don't look like a model, let alone ignored.
The great thing about the solution is it actually makes you healthier and benefits every part of your life. The other great thing about going from fat - fit, is that you know who the shallow people around you are, so when they hit on you, it is easier to ignore them.