it sounds like you know what you want, but are maybe scared to go after it? you say you live at home, and feel like a mooch- if you have the financial means, why not move out? you said you feel like a fake- i havent met one person in my life who isn't faking something. you need to be real with yourself before you can be real with anyone else. i'm in my 20's too, and feel lost a lot... i think everyone feels lost at times.
this may sound elementary, but make a list of things you want to achieve or change, and possible ways to obtain them. getting it on paper can clarify things, and get it out of your head.
you also said you wanted to get fit- it doesnt have to be running a marathon- go for a walk, join a team if you like sports, maybe meet with a nutritionist to talk about a good diet plan.
coming from a girl who was also the "ugly" friend, regardless of my friends telling me otherwise, i completely empathize with your feelings about men and relationships. except i have never been in one, and i don't know which is worse- settling or being perpetually single...
i think you have the tools to fix things, you just need to take it one thing at a time. every day is a new day, and another chance to reinvent ourselves. we just need the courage.