You probably are retaining water....when you start a new workout routine & your body/muscles aren't used to it they will retain a bit of water from being swollen. It'll come off as your body gets used to the workout so no worries
Also try to eat at least some of your activity points....like if I earn 5 points on a run, I will eat at least two of those points in filling foods. Some people don't do it but I have found that works best for me.