200 mgs of Doxy a day only keeps the bacteria from replicating, it doesn't kill them off in high enough numbers to get past the infection. I too hope that your LLMD will either put you on a higher dose or will change abx.
As Barngurl said, that all day walk was too much for you. You are actually quite ill and need to treat your body in accordance as this is a very complex infection, not at all like tonsillitis, or even bronchitis - otherwise you won't be helping yourself heal.
This article might help:
www.butyoudontlooksick.com/navigation/BYDLS-TheSpoonTheory.pdf Hang in there!! Give your body time to heal and you will be back to those long walks on the beach!