Can new pair of work boots cause tailbone pain? stand on concrete 8-10hrs/day. dull ache not sharp. also seem gassier but no pain passing it or poop

Only if you kicked: By them. Shoes themselves would not be an issue but prolonged standing in one position or with improper posture can be a cause of back pain. Try measures like small foot rest similar as to why there are brass rails at a bar ; alternate your standing position. If working over a bench see if it can be adjusted so you do not have to bend over as much. If persists, especially on days off, see doc.