Achy dull pain on right side/lower back. gallbladder? kidney stones? i've had kidney stones once but with no pain.

Hard to say: Kidney stone are usually very painful. Stones, gallstones and kidneys infections can all cause this kind of pain. See your doctor and get checked out.

Right side back pain: This syndrome could be either muscular or renal or gall bladder; gall bladder discomfort associates with fatty meals and can come and go; stone pain usually radiates down flank; if your flank is tender to superficial touch, then a muscle may be traumatized or strained. Of course, ultrasound can evaluate GB and Kidney