Welcome twin, taking that first step to trying to figure out what's changing in your body is a huge challenge! But congratulations for facing it!
I can tell you like Gretchen pointed out, this is a very long road and a wise dr will start at the beginning (the bottom of the list of least illnesses) and work up. There are many many things that mimic MS and ALS and a multitude of others. Try not to project anything disastrous on yourself, it's devastating to your outlook. The way I figured it, the doctors spent alot of money for their educations, let them earn it figuring it out for you. That's why you pay them (and the insurance companies charge us the big bucks).
With all that said, relax and be good to you. Do what you can, keep a journal of how you're feeling and what you're doing, the temps you're doing it in (like the weather and walking and miles and time) etc... that's helpful to the neuro when you get to him. Let the docs ask you for these things, if they don't ask them, if they're not interested, find one who is. It's kind of sad but in my experiences, I found I had to be very persistent alot of the time and make the dr work for me... and if they didn't find the ones who would. There's a trend in drs today to allow the patient to tell them what their problem is, it lets them off the hook so to speak but it shouldn't be that way when you're seeking like now.
Good luck and keep hanging around asking questions. This is a great place for resources and support!
Fear knocked ~ Faith Answered ~ No one was there! :)
~ Ephesians 6:13 ~ * ~ Psalm 27:1 ~