You can also get back pumps from things other than dbol too.
Earlier this year I was suffering from debilitating back pumps/cramps that would force me to lie down and rest my back after just half a mile of running. While lifting, I could finish my squat sets, but would have a hard time walking afterwards. I wasn't on dbol or any other steroid and it came on rather suddenly. This has happened before and really didn't seem to match up to the intensity or amount of weight I was lifting or any particular workout routine.
After trying potassium, chiropractors, and other remedies without any success, I happened to run out of creatine and didn't get anymore for three weeks. Suddenly my back issues went away completely and I could run several miles with no problems. I tried creatine for a few days again to see if it was the culprit, and sure enough my back pumps came back. It's probably caused by the same mechanism as dbol - water retention in your spinal errectors.