Pain that comes symptoms and conditions

I began taking 100 mg x2 per day for ten days for a bacterial infection. I am 48 years old and I have Fibromyalgia and arthritis pain issues as well as other health problems. By day three of taking doxy, my pain issues increased dramatically. My legs burn and the pain the runs from the waist to the heels of my feet are not something that has happened to me before...thus, I surmize it is the doxy. My legs and feet burn and hurt so much that it is difficult to walk and to sleep as even resting them on the mattress keeps me awake at night. I tried taking it with a tbsp. of peanut butter and a small glass of milk and in 15 minutes I vomit. I need to have considerable food in my stomach and yet, I have great stomach pain that comes in waves. This is a very difficult medicine to take!