A couple considerations. If you want a racquet that's "more comfortable", you're going to loose a bit of pop if you're looking for a softer, more flexible option than your Prince. Your frame is already somewhat light, so you're bound to lose power if you go for something lighter or softer.
Also want to point out what might be the real issue for you. If you're getting a tired arm from playing with your current frame, you may want to invest in some instruction instead of a different racquet. Yours is rather light and lively, but from the sounds of things, it's wearing you out anyway.
At your age, you probably shouldn't be shopping for a lighter alternative. Instead, I'll bet that you'd benefit from a little guidance to encourage the bigger muscles in your legs and core to chip in and energize your shots. After a couple hours of hitting, your legs should be getting tired before your arm.
No crime in looking at racquets, too, but I don't know what to suggest given what seems to be ailing you. That Babolat may be a good place to start. If you can afford it and want to look around, I've had a GREAT time with TW's demo program. They sort of give you the keys to the candy store and only charge for shipping. Whatever you try for gear, I strongly suggest you pay attention to the static weight, balance, and flex of everything you sample - you may even want to write it down for reference. We can only tell when we've got that good fit in a racquet when we find it on the courts.
