You have a perfect history for an L5-S1 disc hernation. These disc hernations start with an annular tear which causes central back pain. As the disc herniates, the nerve becomes compressed but will take 1-3 days to develop leg pain. The nerve is tented by the disc herniation so sitting (or bending forward) hurts and standing is better (the nerve is under less stress when your thigh is parallel to your back-standing).
I would be suspicious of your GP’s finding that your reflexes are equal. Almost always with the size of your hernation, the left achilles reflex will be dulled (plus one instead of plus two) but it is a subtle art to determine what the reflex is.
One of the keys is to check the strength of the gastroc-soleus (calf) muscle. This muscle is so strong that manual testing (the doctor uses his own strength to see if he can “break” the muscle) normally is useless so there is a self directed test that can check the strength. See https://neckandback.com/conditions/home-testing-for-leg-weakness/ to understand how to test the S1 nerve.
If you have no motor weakness, I normally advise an epidural steroid injection along with PT. These injections can be very helpful to relieve pain. If the injection helps, then a repeat injection might be helpful in 2-4 weeks.
If however, the muscle is weak, I recommend surgery as the chance of motor strength recovery is much less without surgery than with surgery. I understand this is a national health care country but they should be able to do the right thing. I have talked to prior Australians with this same problem. These individuals were successful (if their GPs would not emergently refer them for a surgery) by presenting themselves to an ER with pain and weakness. The ER tends to understand this dilemma and ask for a quick referral.
Dr. Corenman
Donald Corenman, MD, DC is a highly-regarded spine surgeon, considered an expert in the area of neck and back pain. Trained as both a Medical Doctor and Doctor of Chiropractic, Dr. Corenman earned academic appointments as Clinical Assistant Professor and Assistant Professor of Orthopaedic Surgery at the University of Colorado Health Sciences Center, and his research on spine surgery and rehabilitation has resulted in the publication of multiple peer-reviewed articles and two books.