Angell, With some evidence of blood in your stool, you need to check into an ER. Sorry, but that's the deal. Don't mess with a potential internal bleed.
Pred might not be a drug for you. And, if not, the sooner you get off of it and onto one that will work for you, the better.
My Dad had a GI bleed from Pred, and you do not want to go through surgery. It wasn't a pleasant experience for any of us.
PLEASE, seek out help at the ER! The other reason is that you have signs of an adrenal crisis (pain, sweating, and fatigue are all classic signs). They are BOTH life threatening, damn it!!! Didn't your doc know the signs of that one?
This is yet another case of someone going down from a Pred dose too quickly and having an adrenal crisis.
You'll also want to check in with an endocrinologist after you've been off of the Pred for a while so that they can check your adrenal function. Maybe it's already low or something else is going on.
You know, drugs are okay, but some just aren't meant for certain people. And it's not worth risking your life to have them.
I really hope you'll be okay, and that you can revisit all of this with your neuro. They blindly follow that algorithm, Mestinon first, Pred second, etc.
What else can I say, but be smart! Well, you are smart, but that doesn't always mean acting smart.

Don't push that physical envelope and get a LOT of rest and TLC.
Please let us know how you're doing! We can talk about the sadness of having MG some other time!!!

Annie
BTW, I've had my adrenal function tank. It's not fun. I sought out help right away, as should you (per my endo!). Mine was jet lag induced—yours is more serious.