As you may recall, I am also PPMS, Dx nine mos. ago. I am not taking any drugs (even though all 3 neuros I've seen have wanted me to, but haven't been able to make much of a case), and have been doing the Swank diet since shortly after diagnosis.
I am currently continuing to research PPMS (there are research papers available online) and to look for a neurologist who's a good fit for me. I want to organize a group of PPMSers in Southern California so we can share information, since, as 10-15% of the MS population, we have the least-studied form of the disease, and we need to help each other.
I will try to respond to your concerns here:
butt kicking fatigue
I have a small manifestation of MS-related fatigue, I think. It's sometimes easy to tell that I'm having an inordinate amount of fatigue, and, when that happens, I do my best to REST as much as the situation permits. I am also looking to change my lifestyle to make room for this. I have been working in film and television postproduction, which often entails high-pressure 14-hour days with no lunch break, which are totally out of my control. Thus, I must accept the fact that I need to get a different kind of job. I'm working on it (presently unemployed).
limp when I walk more than a couple of miles. I still walk.
I have the "dragging leg" after about 1.5 miles. It probably appears subtle, but it feels very noticeable. I find that a focused and regular exercise effort makes a big difference. I have been doing short workouts at home with dumbbells, about 4 days a week, and I find that the "spasticity" (stiffness) in my right leg goes away partially or completely after I have a good "leg day" workout (lunges and squats with weight). My fiancee is also doing the women's version of the workout, and she has gotten in much better shape. (She's better about being consistent with it than I am.)
numbness in feet and lower legs
This I do not have at this time. For this, I think, we need progress on the drug front, in neuroprotection and regeneraton. There are promising drugs that aren't too far away from being available.
Do you think it's actually balance -- I mean your sense of balance, like the inner ear function or the brain's ability to process inner ear balance issues -- or is it your legs' ability to keep you on balance, because of MS's effects on your legs? Am i making the distinction clearly?
I have had "balance" problems, too, but mine were because of atrophy in the muscles of my foot, ankle, and calf, I think (and/or possibly because of damage to the brain areas that control them -- or the faint lesion on my spinal cord, blocking transmission?). My balance is just fine if I stand on my left (unaffected) leg. I have been concentrating on getting my strength back in my right foot/ankle/leg, with some success, and it has helped my balance, too. I am taking Argentine tango classes, which demand some subtle and specific things from my foot/leg/balance, and I have made definite improvement. I don't know if this improvement is because of muscle building, and if so which muscles (the atrophied ones, or the ones around them?), or if it's from "brain plasticity," i.e. my brain found a way to re-route some of the pathways. However it works, it follows that the best way to retain or regain function is to work at it.
Yoga is a great idea. You may at some point want to do some Feldenkrais also, for specific problems.
some brain fog
I have some days where I feel like I'm slow or spacey compared to my usual, or compared to people around me. This worries me a lot, though I think some of my perception of it is exaggerated because I'm so worried about cognitive changes. I think fatigue makes a big difference, as does diet. If you've been overdoing it and having, say, a sugar crash, you will be especially prone to being "out of it." Some or all of it could be non-MS related. Take it easy.
Overall, keep being active, but take it easy on yourself.
For you as a newly diagnosed pwMS, I recommend paying attention to how much you can stand of anything, whether it's work or heat or noise or how much you can stand reading about MS, and give yourself permission to do something else. This is a lifelong change, and you need to pace yourself for a marathon and not a sprint. If you are like me, you will want answers ASAP, but as you have surely found, there are no simple answers in MS. It takes time.
I'm still reading up about drugs, the old ones (not the interferons, but still some interest in glatiramer acetate/Copaxone) and emerging ones. I am also pretty sold on the Swank diet, with some improvements and supplements, and it's a pretty easy and broadly healthy way to eat anyway. You'll find a lot of people doing other dietary adjustments as well, some very restrictive. For physicians not to deal with diet at all is incredibly narrow-sighted, and they should be embarrassed. On our side, it's something definitely to address.
In summary, I disagree with your doctor: there are treatments. More treatments, specifically for PPMS, are coming. The hard part is sorting through all the information. Take it at your own pace.