Hi there....I don't have much for you but I know how waiting for an answer can be tough....especially over the weekend.
I do know that one cause for fluid can be ruptured cysts. Cysts are fluid filled structures. Sometimes cysts can develop, they rupture and then the fluid from them is simply reabsorbed by the body. Other times the fluid is not and then the Dr wants to test further. Sorry this isn't much but hope it helps even a little.
Take care. Oh and take it from me...you may want to limit your internet research...there's tons of "not so good" information out there and even the good information can drive you crazy with all the symptoms, horror stories etc. I will keep you in my thoughts.