Hey Lemon!
For the dizzy-when-standing thing, it probably has something to do with your blood sugar. I had the same thing happen to me a lot one time while I was back home in Germany, so I went to the doctor and they said to just take your time with moving into standing positions. Like, if you're laying down, don't just jump up; Sit up for a few seconds, then put your legs on the floor for a few, before finally standing in place for a minute and walking.
As for your joints: You're young, so this is definitely irregular. This could be a sign of a few different kinds of juvenile Arthritis. The first one that comes to mind for me is Rheumatoid Arthritis– Do your research and see if the listed symptoms match yours. I also recommend looking into some other types of arthritis. If your feel your symptoms match what you see online, go to a doctor. They will diagnose you and either give you medicine or another form of treatment. Otherwise, I would try taping, as it is very good for pain relief, or sports wraps. For severe joint pain, you may want to purchase a few braces. Like, if your ankle hurts a lot and very often, try an ankle brace.