Yeah, the feeling that swallows you is that it isn't going to happen. I feel so hopeful every morning, and the doom and gloom as the day progresses.
It's difficult I know, but the best thing you can do is put the visa to the back of your mind, get away from the computer (and/or your phone) and do something to take your mind off it.
Get out and about, spend time with friends and family before you leave, do some things you enjoy in the US which you won't be able to do in the UK, and enjoy the warm weather (it's been snowing in parts of the UK this week... right now, I'm sitting on the sofa, curled up in a blanket). Make the most of the time you have in the US, rather than stressing about the visa
.