I am very sorry you go through so much pain when you are simply attending to hygiene.

If I am recalling correctly, you are challenged with fibromyalgia?

Does the water hitting your skin cause pain?
If so, maybe consider an adjustable showerhead?

Some people enjoy attachments to the pipe that feeds the showerhead. These have flexible tubing and a "wand" at the end where the water comes out. This allows more control of the water and stops the "pelting" sensation you might be feeling from the current showerhead.

There are many styles. You can take the wand out of the holder at the top and hold it in your hand, self-directing the water flow. Can usually also choose from a variety of levels from softer water flow to a stronger flow.

Just one example:

Waterpik 9-Spray 4.5 in. Single Wall Mount Low Flow Handheld Rain Shower Head in Chrome-YAT-963ME - The Home Depot

It's quite possible the shower causes you pain for a different reason.
I truly hate to see you suffering from a shower.