SPD Agony!

Two days into my trail and I discover the limit is coming from an
unexpected place - unbelievably painful feet. I'm using Specialized BG
Comp mountain biking shoes in the appropriate size. When I put them on
in the morning, they are already not comfortable shoes, stiff and
grating over the toes, but as the day wears on they turn into Chinese
torture. This is on a recumbent tadpole trike where the use of SPDs is
required as a safety measure (to prevent running over one's own leg,
which I nearly did the other day). I thought this would be the
ultimate comfort ride as there is none of the pain in the crotch or
wrists that used to terminate previous rides on two wheels. But that
pain was trifling in comparison to this foot agony.

The balls of the feet burn like fire and the toes go completely numb.
Every pedal stroke is so excrucuating that I have to stop every 3 km
or so just to try and get circulation going again. I cannot walk in
them at all - very slippery and stiff, despite the fact that these are
supposed to be used on trail where one is often off the bike.

I tried putting a wad of kleenex between the lining of the shoe and
the SPD clip. That improved matters slightly, but I still cannot go
more than about 10km without the most agonizing pain. And the pain
lasts for about half an hour even after I have taken the shoes off.

Also, clipping and unclipping is a chore. I thought it would get
easier. But it can take me several minutes to clip and unclipping can
be even longer. The fact of having to press down into the core of the
pain to twist the feet off the pedals is part of it.

Is this normal? Is it something "you just get used to"? I don't want
to take risks with my feet as I am borderline diabetic and this looks
like the fast route to amputation.

Your experiences?

Thanks.

EFR
In deepest Provence