Hi James from Missouri,
First of all, welcome to the forum! It's good you are taking Doxy as I took that antibiotic but I wasn't diagnosed early, actually, it was 5 years after I was infected that I was "officially" diagnosed. I did so much research and knew I had lyme but needed medical proof.
Anyway, it sounds to me (I'm not a doctor) that what you are experiencing is toxins in your body from the bacteria being killed off. When bacteria die, they always leave toxins and the body needs help ridding itself of these toxins or poisons.
Did you read my post about detoxing? I remember when I first heard the word "detox" from others, I thought they were nuts! Back then I just "assumed" that our bodies automatically detoxed by itself, boy, was I wrong!
Perhaps first try with a detox bath and see how you feel? You also may be interested in reading this article:
Hey, if I could get better, anyone can!
Hope you feel better,