Doctor Rx'd me Medrol 4mg 6 day taper therapy. Side effects?

I was prescribed to Medrol Dosepak for 6 days, first day is 6 pills, and tapers off one pill a day. Total of 21. Im 15, and tall and weigh about 180, I'm working on getting more fit for the summer, and i heard that medrol can cause rapid weight gain, and that'd interfere with my goal. For anyone who has taken this, how strong was the weight gain? or appetite? If it's only the appetite that causes the weight gain (something i can control) I can man up and just continue my diet, but I was wondering if its something chemical for example the adrenal gland would slower my metabolism or something. Once again, for anyone who has taken it can you tell me how your weight thing was going on? And any other comments about your experience. Thanks ! Best answer will be given to whoever can answer my Q's.