I was young, buff and strong as an ox. Within days after coming down with something similar to Mono, I couldn't walk up a flight of stairs without sitting down.
You will find many, many people who can and will relate to your situation. Unfortunately, for me, I had to figure it out for myself.
Here's my two cents:
If you're not sleeping, this is paramount that you get this figured out. Your body cannot heal without proper sleep. I take 50 mg of Doxepin each night and I saw an immediate improvement in my sleep (I was no longer feeling "wired" while trying to sleep).
I made the mistake of "pushing myself" physically and thought I was invinceable. I should've dialed everything back immediately.
I was an "A" type personality, I learned to only worry/think about things that are truly important, not petty issues. I avoided stress and drama, it makes a world of difference. I became more selfish, because I had to be. It's ok, take care of yourself first.
I should point out this happened almost 25 years ago. I was very sick for about 2 years. I limited myself for another 2 or so. Everyone is different, trust your own instincts.
I would occasionally have "flare-ups", but since my Celiac diagnosis 5 years ago, I have had none. I can't draw a conclusive correlation between gluten and CFS, but I always felt it "was something chemical within me", as opposed to arthritis or something.
Good luck. I'd be happy to assist you in any way. Just ask.