I'm sorry you're having so many problems! I know that August 15 seems like an eternity away.
You talked about having shingles. Do be sure to tell the neuro about that. And you might want to ask about the possibility of having a recurring chronic infection of the central nervous system - -something a neuro might not be able to discern but you'd be seeing someone like a rheumatologist or infectious disease specialist. The fact that you're having problems related to the shingles, in conjunction with all the other issues, seems to me -- and note, I am NOT a doctor-- that there might be some connection between the shingles and all the rest of the symptoms (and not necessarily MS.)
I'm not sure what the skin testing is about. That isn't anything typical for MS. You might want to ask your doctor what he is looking for. The only skin testing I know about are for allergies, or tuberculosis, and I don't think either of those could cause your problems.
The bladder problems can occur with MS..but with other problems, too. Be sure to tell your neuro about that, too. There are meds you can take for that, but generally doctors will want to find out why you're having the problems, before they start treating it.
Yes, a spinal tap could be a useful diagnostic tool. It could indicate MS...but it could also indicate whether there is something else going on that the doctors need to look for.
Do come back and let us know how it goes!
...I am not a doctor, nor health professional, and don't pretend to be one, here.....