I hope you reported the injury and filled out your paperwork.
Hi man
your symptoms is very close to radiculopathy of spinal nerves. It seems after your brief back discomfort at work, your spinal nerves could not regain their normal conditions. Sometimes pain and numbness of spinal nerves is not located over your back. They may be manifested in the nerve end organs. your left thumb is related to your Sciatic nerve field. So I think it is related to your sciatic nerve that is originated from your Lumbar and Sacral nerves (L4-5,S1-2). If your symptoms are not complicated with movement problems, you can manage them with physiotherapy or chiropractic. But if you have problems in moving your thumb please put it with an neurosurgeon.
god speed you.