I was going to suggest that you might be digging in too hard on the strings to hear yourself? That will cause cramping. Bring up your stage volume so you can hear yourself clearly and then playing with a lighter touch. My guess would be since you are performing the song live you have already played it over and over again in rehearsal or on your own and are able to get through it. Live you should have the same results. good luck RTS
The issue seems to have gone away as I've got more use to gigging now, seems it was actually just nerves haha, still as useful tip though thanks!