I am a 23 year old female and I had to comment because your story sounds a lot like mind. I in fact just went to a urologist and they did an ultrasound on my renal artery, kidneys, and bladder. They also did the same procedure that you were talking about where they insert the cytocope (sure I am spelling that wrong) in your uretha. Talk about being uncomfortable. Guess what? My tests all came back normal as well. Like you, I asked the doctor, "well why do I still have this dull back pain that sometimes moves to my groin?" He said well I really don't know. Like you, I was expecting to find the answer. I thought for sure they were going to find some sort of kidney disease, bladder problems, etc.
Like others have said, I think it is completely normal for people (esp. men, because I have seen it when my b/f goes to the bathroom) to have bubbles in their urine. As far as the eye floaters, get them all the time as well but I had my glucose checked and no diabetes. My doctor told me that as we go through each decade through the aging process, we will start to experience new aches and pains that are normal. It's just a part of life.