sourish smell only under 1 arm

Name: 
alex
More information: 
Hello, Only one of my armpits have a sourish smell to it I've never had this problem, I'm not a sweaty person but as well only this arm gets a little wet down there once i begin full movement. I've tried 4 different deodorant brands as well 5 other soap brands. I'm not sure what else to do as this problem is slowly killing me. Please can you help me