Weight up by half pound could mean a few things: you gained a bit of muscle, increased water retention/hydration, glycogen stores, full bladder or bowel, some undo tested food still in your Gi tract, etc.
Your waist going down a half inch means you lost some water weight around your waist or fat.
Both are important indicators of what's going on. The biggest change at the momen would be the waist size going down. That's great news! The weight going up could just be you didn't go to the bathroom prior to weighing yourself or you gained some muscle.