Peadar has a good point on his post - what else do you do?
I have two instances where I've had problems:-
One was having limited space at work and the pc tower's fan gently whirring was triggering muscles when I was touching the desk so extreme tiredness felt after playing for a few minutes. Putting the tower on another table resolved this instantly.
The other I'm still going through.
I have recently moved and have a Leylandii hedge to remove. I've done this in stages but wielding a pick axe and digging out roots with a crowbar really causes pain around my elbow joints. This is exacerbated by then sitting down and playing for periods of time.
Thankfully I'm coming to the end of the hedge, and also realised that doing it in stages meant my arms recovered, and also not to play for longer periods again to let my arms recover, which thankfully they are.
At times it's worth taking an overall holistic approach if you are experiencing discomfort, as the melodeon might be reflecting a problem caused elsewhere.
Q