How can you say this? No a curve thrown properly and given the person has matured enough to throw it, it shouldn't hurt.
Back to your question pilldom.
You don't want to throw the slider that will screw up your arm, but chances are you don't throw it properly or hard enough yet to feel the pain in your elbow. This is common and we get this a lot kids around your age throwing sliders. I'm 15 and even when I throw a slider just once on accident, I throw a cutter that's close to it but when thrown improperly can easily change into a slider, I feel the pain in my elbow. Once you throw hard enough you'll feel it, so drop that pitch. I'd drop both the curves if you say it hurts.
I wouldn't keep the knuckle ball. This is a hard pitch to master and keep. It's also not effective unless you have a ton of movement on it. A good hitter will pick up the lack of spin on your knuckle and it will be like knowing a change-ups coming and they will blast it.
Circle change is a good pitch to keep. If you have trouble with that you can always go to a 3 finger change-up. Sometimes you need bigger hands for the circle change.
So my hints to you. Get your mechanics down. Master your 4-seam and 2-seam's locations. Work on the change of speed for your change-up and to keep it low. At your age no need to worry about horizontal location for your change-up just keep it low to start off with.
That right there is a lot to work with and will keep you practicing for a long time. Maby in a couple of years you can start to throw a curve, that will be your best bet. A cutter is also a common pitch to start in a couple years and a lot of kids throw it around here and same thing with a splitter. Quite a few kids have these pitches and like them, but my suggestion to you is when your a little older learn the curve and if you have trouble you can always go to a different pitch.
That's just my 2 cents