How To Stop The Sweaty Sweat Sweat! :D HELP!?

Hey so i am a 15 year old guy and i am in need of serious help! Well not really, but it's gross and i need to get rid of it. I sweat through my arm pits which is normal, but it tends to soak through like 2 shirts so i don't know what shirt to wear to work out because that's gross. Also i tried white shirts because they seem to not show the sweat so much until i realized there are gross yellow stains on them! How do i stop this from happening!? Also my hands sweat a lot! I get nervous because they sweat and they sweat because im nervous, (ironic), and i tend to get nervous that girls will be like, EWWW!!! so what do i do!?!?!