Just for "fun," I did a community search of the words "roller coaster." A few hits are linked below at the end of this post. So know you are not alone on that front!
I am taking zith and have taken plaquenil. I also have experienced feeling better off, or at reduced, treatment, only to yet again Herx when treatment resumes or increases. The interpretation of this pattern is that you are still sick.
Recovering from Lyme is not a linear improvement. Given the natural cycles of the bugs themselves, along with the Herxheimer reactions, it is expected that you'll go through ups and downs. I know how emotionally frustrating that can be, as it really complicated ever making plans because of how unreliable it makes us.
As we often say around here, grasp onto the good days and gut it out on the bad.
Do you have co-infections? My LLMD uses the zith to treat my Bart. Plaquenil I've read to be effective both against Babesia and the cyst-form of Lyme disease. But always ask your doc to clarify what med is being used for what bug/reason. If you are having Herx reactions, I wouldn't worry about it not being strong enough. But perhaps you are questioning if your worsened state is due to Herxing or just active infection. That's always a tough issue to decipher, and sadly, other than patiently waiting for improvement, I don't know how to test it.
Here are some "roller coaster" posts from the past:
http://www.medhelp.org/posts/Lyme-Disease/Roller-coaster/show/1126486
http://www.medhelp.org/posts/Lyme-Disease/Flare-up-yesterday-and-today--What-gives/show/933201
http://www.medhelp.org/posts/Lyme-Disease/Doubts/show/944319
http://www.medhelp.org/posts/Lyme-Disease/The-Roller-Coaster-Continues/show/762426