Doxycycline Monohydrate and lyme

I feel like I am SO tired on doxycycline. I'm on it for Lyme disease, had Rx for 3 weeks, was off it a week and started to have the joint pain relapse, so now I'm on it for four.
It seemed that I was finding myself with very shallow breathing too. It seems if I forget to take a dose or two, I'm not as tired.
I'm less focused and more forgetful, it's hard to get things done.

I am being treated for lyme disease with 400mgs/day. I take 200mgs in the am and 200mgs in pm. The course of treatment is for 4wks. I am in my 2nd week. I feel just awful. My side effects are nausea, generalized weakness, fatigue, abdominal pain, headaches, joint pain and stiffness. I did not have these symptoms (except joint pain) till I started the meds. I feel worse now than before I started this medication.