Can a kidney infection cause intermittent pain in side/flank over several weeks Pain getting more constant and stronger but urine clear on dipstick.?

More testing . if the dip stick if negative then there is a low potential for a kidney infection although a urine culture sent to the lab is more accurate.
Kidney stones can cause this type of pain in absence of an infection an X ray or a CT (more accurate) is used to diagnose stones .