My band has it days... sometimes too tight, sometimes not tight enough. I've learned to pretty much relax and go with it. BUT, I'm not having back pain or any other pain issues. I once was so tight I couldn't get fluids in, and that was too darn tight.
Please talk to your doctor and if he unfills you to 8cc, then look for other answers like low carb, more exercise to help get you through. Sometimes you have to give yourself and your band a little time off, and that has often been the "cure" for the very few issues I've had.