I also had blood tests (for HSV, HIV and syphilis), these also came back negative. I have taken a two week course of
doxycycline and a week of metronidazole (not at the same time). My symptoms neither improved, nor subsided with these antibiotics.
I am very anxious about both what is causing this symptoms and if I will be able to get rid of them. Not having a diagnosis is also very frustrating, as I don't know what can be done to move forward.