I had the same experience with Decadron back in the late 80's. I ballooned up, literally overnight! It was awful!
One of the best things about WW is that they teach you how to get back on the plan if you have a bad day. As dieters, we are very bad about throwing in the towel too quickly. We start off our week fine, get to mid-week and something causes us to go off our plan - unexpected stuff at work, extra stress, etc. Our response? We just say, "to heck with it!" and vow to start again on Monday. We don't have to do that. As my WW leader says, if you drop an egg on the floor, do you throw the rest of the dozen on the floor, too?
Just take things one day, one meal at a time. The biggest motivator for me is seeing that scale go down. Also forgiving myself if I screw up, and having the courage to get back on the plan. Nothing, and I mean NOTHING, tastes as good as seeing that number on the scale get smaller and smaller.