I'm not medically trained, but here's what I find on the internet for your consideration:
Plaquenil is a drug use
d to treat malaria and
also in autoimmune conditions such as lupus and
The references I have found as to using it in Lyme treatment combine Plaquenil with another medication at the same time.
I wonder if your doc is treating you on the assumption that you have an auto-immune disease and
not a bacterial disease -- ?