Sorry things are going badly for you. It sounds like your ID doctor may not be very knowledgeable about Lyme disease. Four weeks into treatment is a very common time for a flare up of symptoms.
This is known as a herxheimer reaction. As the bacteria are killed, they release toxins that cause symptom flares. Four weeks is a classic cycle.
Now, I'm not a doctor, so I can't say for sure that is what is happening for you. But I am a bit concerned, because steroids are containdicated in the treatment of Lyme disease.
Steroids cause a suppression of the immune system, allowing the Lyme to get a deeper foothold. they are only used in dire emergency by doctors who are Lyme knowledgeable.
Benadryl, on the other hand, has been used by many on this board to alleviate the discomfort of a herx.
I suggest you do a little reading about Lyme, to educate yourself. Treatment for Lyme is very political, and not all doctors agree. But you may decide you need a doctor who knows not to give steroids with Lyme!
If you do, post in the section Seeking a Doctor and people can send you the name of recommended doctors.
Here is some info to start:
Dr. Joseph J. Burrascano's Treatment Guidelines
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Sonoma County Lyme Support
[email protected]
Hey,
So sorry you you're going through a tough time. I was on one month of 2 grams of Rocephin every day. I too had a relapse of symtoms around week four and was told it was from die off toxins.I was told by my home care specialists that it was a text book response, and not to worry. It was a short lived set back, and I was fine. I went on 400 mgs of Doxycycline for two months. A week after I stopped the Doxy I was back to the same symtoms you have and crippling tendonitis, as well as flank and rib soreness.
I was put back on Doxy, at the same dose. Slowly I am getting better. Headaches are gone, flank and rib pain is gone. I can still barely walk in the morning, but I loosen up later on in the day.
I don't think I'm cured yet, but it's under control until I can find an additional treatment.
I'm in waiting mode for someone who I'm not sure is llmd. No one here seems to have heard of him. Can't see him until Jan 31st.
Good luck. I bet it's just a normal set back. But don't take steroids. They are supposedly no good if you're already immune compromised. At least that is what is repeated on LymeNet and in referral sources.
When you feel bad, rest. You'll find it pays off. Your body will alert you if you're doing too much.
Meem
Keep reading and learning all you can. When you are ready for more, ask. Treepatrol has a great page of links, but I won't inflict that on you quite yet. 
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Sonoma County Lyme Support
[email protected]