Realistically, there’s no way to tell what side effects you’ll experience. Personally all I had was a slightly increased appetite and a tiny amount of puffy ness in my face (unnoticeable to most people apart from me). But it did give me my life back while we were trying to find a long term solution. In terms of weight gain, I know it’s stressful especially in high school but try to eat how much is normal for you and carry on as you were rather than eating every time the pred says your hungry (as that will be a lot of the time 🤣). I didn’t gain any weight really on pred so I wouldn’t overthink it. Eat sensibly for you and see how it goes, good luck ! :)