Originally Posted by Irishbc
Stop getting punched...
No seriously though, it's not the jabs guys, it sounds like you're too tense and hunched over when in your fighting stance, try relaxing a bit more, as well as stretching and warming up your back properly.
If you are too tense and crouch your head and back this could certainly be the cause from the stress you are placing on your body. Make sure you are fairly loose