Lower back pain lifting heavy stuff, it was pretty bad. It has happened again, chiropractor was a big help. Should I see a specialist & have a X-ray?

Perhaps. Vast majority of injuries to lower back following heavy lifting reslove with time, rest stretching and strengthening excercises. X-rays are done to rule out frature and will be negative in most of cases. Most likely you did not recover your strength in the back muscles after the last treatment so make sure you rehab yoursel this time if it occurs again then see specialist.