That's frustrating, isn't it, when a doctor tells you there's nothing wrong and you know there is. How condescending!
It makes me wonder about allergies... my husband's mother gets a hoarse voice/strained throat when she eats dairy. She goes to a naturopath who helped her figure that one out, and also gives her herbs that help tremendously.
On a side note, for a while I had very frustrating recurrent tonsillitis. I had a cycle of getting sick, taking antibiotics, getting better, and then 2 weeks later getting sick again. When I got pregnant and didn't want to mess with antibiotics one more time, I asked my midwife what to do. She told me: take a fresh daikon (Japanese radish), shred it and put it in a strainer with a bowl underneath. Add salt and honey. Let it sit for a day, then drink the liquid in the bowl. I got as far as buying the daikon, never tried the remedy - if you try it, let me know how it goes. What actually did work for me was another of her suggestions, gargling with lemon juice several times a day.