Honestly I have had a couple of pretty weak days. But I just took those days fairly slowly. I made some warm lemon or lime water and I was okay after a little while. I do have to conserve my energy and be careful not to overdo things.
Then again I have had times when I had a tremendous amount of energy.
I think being cold all the time and nauseous in the morning are the two things that I have had to figure out how to get around. I started to get up earlier so I have more time to get ready, and I haven't taken off my jacket all month! :o)
There are hard times, but the benefits are so worth it. Just learn to roll with it and you will do fine.