How can I enjoy myself and not feel down and nervous?

I had a nice getaway week end with my boyfriend and should feel happy about it. We went on a beach and I was happy to swim etc, but after a while I feel ugly and disgusting compared to other women on the beach, and I just feel like hiding home and hide. I just feel indecent about enjoying myself while there are far prettier women out there and this makes me feel very down :-(.