Is this anxiety or am I just being hard on myself? I feel like I am missing out?

I am a very social person and personable/outgoing as well. I get in moods where people ask me out and I don't go. I am single and in my late 30's, unemployed now and just get unmotivated. Tonight a girlfriend asked me to go to a birthday party in Malibu at Moonshadows..I don't know anyone going- she is driving with another girlfriend- and it's a very upscale kinda place. To be honest I didn't feel like getting dressed or spending money on drinks. But, now I am home alone. I do this to her alot lately. She is always going to places to network or parties and I somtiems say no- then feel like I am missing out. Whats wrong here? I go out alot- but it's up and down. Am I over thinking this? I feel like I am also not skinny enought to wear the trendy clothes that everyone wears when going to these places- upscale. But, I could meet a man or an employer- should I go to these things?? help?