I've always have been in servers on HiveMC.com And then when i was playing a game of cowboys vs indians, my skin turned into a steve some one please help!
Mojang skin servers may be down.
You can check on https://help.mojang.com/
Make sure all services say "This service is healthy. All is good!"
Otherwise, It might be a mod you are using or someone in your account changing your skin.