Sounds like you really need to be talking with your neuro again, and get back on something to slow down the progression. You're very young to be having to deal with this, and you should try to do whatever you can to treat this disease. Sure, the meds have side effects, but -- and I speak from experience here -- the side effects are minor, compared to what can happen with you if you have a major exacerbation!
The heavy legs and fatigue are very common with MS, and unfortunately very hard to treat. There are meds for the fatigue, but they don't work for everyone. The heavy legs is something you might just have to learn to live with.
Good luck with your neuro appointment. Be sure to tell him about this newest flare.
...I am not a doctor, nor health professional, and don't pretend to be one, here.....