Have you read any of Freddd's posts on potassium depletion and B12, folate etc.? If not, you probably should. Here's one link:
http://forums.phoenixrising.me/index.php?threads/active-b12-protocol-basics.10138/
I had been taking B12 in various forms for over 20 years but when I started taking methylfolate 6 years ago, it increased my energy markedly - for about 2 days - and then I hit a wall, with severe fatigue, but thanks to Freddd's posts I realized my potassium had tanked. One of the symptoms of low potassium is fatigue. So instead of cutting the folate, I started taking potassium capsules, probably 400 to 600 mg. in divided doses, the first day, and worked up to 1000 mg. a day, and the fatigue went away. I've learned since that time that I have to keep taking extra potassium every day, and many here on the board do the same.
I think it's very likely that your extra fatigue when you try to increase the Bs is due to low potassium.
Also, ashwagndha is a diuretic - which means it can be depleting your potassium as well. I experienced this recently with an herb I took - horsetail (was taking for silica content), which is also a diuretic. And I ended up getting very fatigued on it and it took me a while to figure it out.
This mentions some interactions of ashwagandha with other substances, including lowering potassium:
http://www.livingnaturally.com/ns/D...ED3918A8&DocID=basic-interactions-ashwagandha
I currently take 800 to 900 mg. potassium gluconate in capsule form a day (in divided doses - it's not good to take a huge amount all at once), as well as 1 or 2 glasses of low-sodium V8, which has 900 mg. potassium in an 8 ounce glass. Some people on this board take even more and of course some don't take any. We each have to find what works for us individually.