Lower left abdo pain. 33 yr old m. blood tests ok, ultrasound - no hernia, colonsocopy found no diverticulitus, very regular normal bm's. dull ache.

Lots of options ...: Abdominal pain can be caused by many different conditions: there are a lot of structures nearby such as the colon, kidneys, ureters etc. If the dull ache is linked to movement, then it could also be muscular +/- trigger points. Sounds like you've had quite a few normal tests so far, which is reassuring, but you should continue to follow up with your doctor if your pain persists. Good luck!