Is the knot hard like a small pebble or feel kind of soft? By soft I mean it still feels round and semi-hard but if you touch it there is a give. Alot of people (myself included) have lipomas. Fatty deposits under the skin that develop for no particular reason. It can be hereditary. I have a couple on my back, pea size as well. One that really bugs me is right in the middle of my back along my spine. Doctors usually don't remove them unless they grow too large or are painful. It may ache sometimes as well. If it is hard, like a rock underneath or you can see it growing larger, get it looked at.
okay so i also found a knot on my lower left side of my back. but whats odd is that it kinda moves around when you push it. its weird. its starting to get painful from me pressing on it now. -E.H
I have the same knot on my lower back on the left side and im not sure what it is or what it is caused by but it hurts to touch it at all but mine is the size of a golf ball and is hard as a rock and moves when I press on it... very very painful