Your embouchure is weak, it's as simple as that. Nothing to worry about, as a new player, this is to be expected. Everyone starts out this way. The number of subtle changes going on within a Saxophonist diaphragm, lungs, throat, mouth, lips, and total airsupport/flow is as great if not greater than that of an Opera singer. Once you start to get some sort of handle on your breathing , air support and embouchure development (and this will take time, and PRACTICE) you'll find that the upper range on into the altissimo is assisted by breathsupport and shaping the back of your throat, NOT changing your embouchure or biting. But altissimo will come later on. Get the book ART OF THE SAXOPHONE by Larry Teal. This book discusses at length much of what you need to know, and has some exercises you can use to develop the muscles used in forming a proper embouchure. Keep it up, and you'll get the hang of it.