Since your Dr has given you the clear, I'd like to take this opportunity to offer a few suggestions. More to look at, rather than instructions.
Make sure your fluid intake is adequate. I'm not sure of all the meds you're on, but it isn't uncommon to find your kidneys producing a bit more fluid.
Don't over do this. Just be sure you're hydrated.
If you're one of those who thinks salt is the devil's own poison, then try taking small amounts with food. But be careful and remember, the devil's own poison is Mushroom soup.
If you feel a bit feint can you try eating a chocolate bar, Mars is a a particularly good one as it has a lot of different sugars. If you're worried about your weight, eath only half. But I'm pretty sure you won't gain extra weight, certainly not in the short term.
If you find the chocolate does help you, then you should try to carry some. But remember, it's the sugar you're after and taking it in different forms, such as is in a Mars bar along with some fluid, like water, should give you the relief you need.
Addition. Just had a look on Wikipedia and I think, on your side of the pond, you might call a Mars Bar, Milky Way. Anyway, these are the descriptions so you should know what to look for.
Good luck.
http://en.wikipedia.org/wiki/Mars_%28chocolate_bar%29http://en.wikipedia.org/wiki/Milky_Way_bar
