I had a ct scan recently the scan didn't show anything.i am confused because i have a knot under my ribs on the left side.?

How far under?: Assume your ct was of your ribs. Then "knot" to which you refer is most likely muscle spasm (if painful). The most common non-painful knot would probably be a lipoma (benign fatty tumor) but other causes exist such as abscess, tumor, swollen lymph node have your doctor explain to you what his/her thinking is about your problem, don't just settle for 1 test & a brush off, if that's what's happening.