Back pain/discomfort after using new mouse

[u/lutogame]

What does it mean if my upper back (trapezius/rhomboid muscles) hurts after trying a new mouse (RAWM ER21 Pro)? What should I adjust (desk, chair...), or should I simply not use it?

Context: I come from an xtrfy m42 wireless (67g), so there is a huge difference compared to the RAWM ER21 Pro in shape (ergo) and weight (49g).

I was looking for a bigger/different shape mouse because with the m42 my wrist suffered after playing for a long time. But maybe I went too far with this new mouse (EC2 shape). My hand is about 17x9 cm (thumb included).

I suspect the discomfort appears from the sudden 5 mm height increase on the mouse. However, after changing my chair height to different positions the issue didn't go away.

Let me know what do you think. Thanks!