This is something I experience quite often. I've always had insomnia as long as I can remember (dating back to elementary school.... I'm a bit high strung!). I've been having terrible insomnia lately, and I figure it's related to the high dose prednisone. I am on night shift right now, worked until 7:30 this morning, haven't slept a wink, and I'm back tonight at 7pm for another 12 hour shift. I feel a flare coming on!!! My rheumy prescribed xanax, but I never feel comfortable taking it when I have to work the next day. But I was having that same exact exhaustion as you, would go out to run an errand, then halfway through just feel like a train hit me, come home and not be able to sleep. Maybe you could ask for a xanax or tramadol script
...? Hope it gets better for you
MJ