One injection a week, to start with, seems high. Some guys do that, but only after trying for example once every three weeks, or once every two weeks. It depends on your dosage.
Be careful with dramatic changes to your body too. Exercising every other day works just as fine I believe and you certainly need to eat (otherwise how are you going to mantain growing muscles). With normal exercise this shouldn´t be happening though. It´d be wise to ask an endocrinologist.
You are 22 and your own person, so you can do what you like, but you do know that your parents will find out at some point (I think that if you take weekly injections, your changes will be rather fast).