Hey there -
I can't say i know exactly how you feel but i do have an idea.
I have clinical depression which can cause extreme fatigue - there use to be days that i couldn't muster the energy to get out of bed.
I'm not in anyway suggesting that you have depression but it might be worth having a quick look at some web site such as beyond blue (
http://www.beyondblue.org.au/) if you have been expriencing low motivation for life, low energy and a general dullness in terms of emotions.
What i would suggest though is that your diet may not be as good as you think. I recently kept a food diary for a week and i was discusted with the amount of crap i was putting in my body. Give it a go even if you think your brilliant and then review it at the end of the week....you might be surprised.
Another thing is water. What you are experiencing may be a result of dehydration. On the days you are training make sure you have at least 2L of water before hand and that you keep away from coffee and soft drinks.
Lastly, try eating meals high in vitamine B a few hours before hand. My understanding is that Vite B is great for energy. I personally eat a couple of Vegimite sandwiches (yes i'm an Aussie and i think it tastes great) and have found it helps heaps.
Oh....and go to another doctor for a second opinion
I hope some of this helps...i know it helped me.
Best wishes