Caroline, I am very glad that you found us, so welcome
With Lyme, most doctors are unsure as the best way to treat it so please don't be discouraged by what they have told you. Many of us here do trial-by-error and find that what works for some doesn't work for all. But don't let that discourage you from seeking resolve to your illness.
As far as memory, I personally had great success with Curcumin. It was suggested to me by someone here and within a few weeks I could see dramatic improvement. Turmeric, which has curcumin as its main ingredient works too but not as much because of the lesser amount of curcumin in it. Curcumin is more expensive than Turmeric.
Something else to try is magnesium. I recommend magnesium L-Threonate as it has been found to help with short term memory. Not all magnesium are alike so stay away from the cheap ones like magnesium oxide.
I am taking Rifampin for Bartonella and it has helped me in my memory and cognitive functions the most. Although I have no proof, I think it has helped with the inflammation and plaque in the brain. When I stop taking it for a few days my memory fog comes back and so do the headaches.