By the description of your symptoms, you could have neurogenic claudication (but you need to see a qualified medical professional to have this diagnosed). This is a set of symptoms caused by spinal stenosis- the very common narrowing of the spinal canal caused by chronic degenerative changes that most of us get over time.
If this is the case, the reason you feel better “bent forward” is that the spinal canal changes in diameter with forward vs. backwards bending. When you bend forward, you increase the volume of the canal and reduce the “pinching” of the nerves. When you stand up, you effectively bend backwards which causes narrowing of the canal and compression of the nerves.
The epidural injections can be very effective to reduce symptoms of this condition but eventually, these injections can become less effective over time. Losing weight can be helpful but will not change the mechanics of the spine. Flattening the back when standing can be effective and is a useful physical therapy tool.
Eventually, this condition might call for surgical decompression. Do not hesitate to get an opinion from a spine surgeon or neurosurgeon.