Is could be a result of contaminants in the meth or nutrient deficiency from bad lifestyle from doing meth ie. not eating enough and/or a bad diet. Either way the common denominator is likely to be the meth and symptoms like this are usually a sign quit for awhile or at least cut down.
Almost definitely from the meth, but probably mostly because of malnutrition and sleep deprivation rather than directly from the drug itself.
Aside from quitting meth, making sure you're getting as much food and sleep as possible and taking a daily multivitamin will help minimise these effects...