I'm sorry you're having so much difficulty! How much of the probiotics have you been taking? I take 120 billion of regular acidophilus, and then a bunch of this other kind with a bunch of different strains (not sure what the dosage is off the top of my head) and I've still had trouble with yeast. Is it possible that you haven't been taking enough? Or maybe the kind you're using isn't the best for your needs?
I know this is stressful, but you will find the right combination of remedies that work best for your body. Unfortunately sometimes it just takes a while to figure out just what that is. I've heard that the time released doryx is easier to tolerate than regular doxy - maybe that's an option?
You may also want to try bringing a copy of Dr. Burrascano's guidelines for treating Lyme - there's a whole section in there that breaks down what antibiotics can be used effectively, what to use when one antibiotic fails, etc. (this is assuming your doctor follows these guidelines but I'm under the impression that most LLMDs do?) Here's a link if you need it
http://www.ilads.org/lyme_disease/B_guidelines_12_17_08.pdf
Good luck - I hope you feel better soon!