If you read my thread carefully, you will see links to places that give
food options. Eggs and dairy are very low in magnesium. So that should not
be an issue for you.

It is not normal to have diarrhea so often. And it is puzzling why diarrhea
aggravates your PN. Diarrhea will reduce potassium levels and over time also
magnesium. It is also dehydrating.

I think you should consult a gastroenterologist and have some work ups done.

Topamax can cause acidosis, and that should be tested for. Acidosis can cause diarrhea. The doctor can do a blood test to measure bicarbonate and tell if this is happening to you. (it is a VERY common side effect and serious).
http://www.medscape.com/files/emedicine/topic312.htm
McNeil sent warning letters to doctors about acidosis (low bicarb) side effects, so your doctor should know this fact.