A 15 pound increase in 2 days?

Hello, so I've tried losing weight before, and because of my new job ive been getting great exercise 5 days a week(FedEx pack handler). I'm around 340, and for a week got down to 335, however on Friday going onto Sunday I feel AWFUL, I'm bloated, my wrists went up in size, and I haven't eaten today and have been feeling full, also threw up today while driving. I went up to 350, and I got horrifically sad, is it water retention? I've been eating better also recently, and I just don't know why on the sudden increase.