That's your problem, not your size or shape. For all they know you are secretly bedding beautiful blonde babes at the beach!

You have to invite yourself along, tell someone in the group you are coming too/would like to come where's everyone hanging this Saturday night, etc. Listening to others talk about what they do without telling anyone what you were doing instead or expressing a wish to have been there, what are "we" doing this weekend, etc. You have to ask for what you want, no one is just going to hand it to you, no one knows you want it!