A lot of times, your mucus gets thicker when you ovulate. If you've tested negative for everything else, it could very well be that. When you ovulate, your mucus gets thicker, getting your body ready just in case.
I just went into the health department 2 weeks ago to get tested.
They said physically everything is fine. No gon. no chlam. no syphillis. yeast infection or trich.
Today was the first time iv'e had it in a while that i can remember and its been about a day and a half since my last period. but I will go into the doctor and keep track over the next couple of weeks. thank you.
Have you been tested for anything else like yeast or bacterial infections? Have they examined your vaginal secretions under the microscope to see if you even just have an overgrowth of the "good" bacteria vaginally?
You might also want to try keeping a diary of when it's happening. If it's happening mid cycle it could very well be related to ovulation. closer to your period only can also be hormonal.
grace