Your flat back may be causing your issues.
Why this matters:
When your low back is too flat, it can lead to a posterior pelvic tilt or vice versa. Having a flattened back on occasion isn’t a bad thing, but look at the position of your vertebrae. They are flexed, or “rounded” compared to neutral (slight curve) or arched (big curve). Spending too much time in this position can cause a weakening of your lumbar discs and possible disc herniations. Disc herniations can lead to pain such as sciatica.
Action steps:Correct your flattened back by sitting your weight onto your sit bones. Something like this video. Another action step you can take is by adding an hour of standing to your day. You’ll notice your symptoms are better.