What could be the cause of extreme pain in lower spine at the coccyx? hurts after long periods of standing/lifting/etc

Coccydynia: http://www.ncbi.nlm.nih.gov/pmc/articles/pmc2682410/ here is great resource of information. Hope you feel better. A local interventional pain management doctor will have several options at their disposal for you to consider.

A few things: Pain can be simply muscular or be coming from a disc problem. True coccyx pain is usually when sitting. An MRI could help if you dont get better with simple treatment.