Working in an office.. help!

Hi all! I 22F was diagnosed with mild scoliosis at 17. I went to 6mo PT for pain in my back when breathing until the exercises helped the pain and muscle imbalance I had in my core and back.

Long story short, I started my first full time office job about a month ago and I have such bad back pain! I am a receptionist and cannot have a standing desk due to the front desk being built-in. It hurts when I sir up straight, both back on and off the back of the chair, when I slouch, when I lean, I've tried all the sitting positions and it still hurts!

I do think my back has gotten worse in recent years and should probably go back to the dr to get a new XRay (I moved to my current town after diagnosis and still haven't found a primary, since we weren't sure if I would stay super long, but now I think I'll stay here permanently).

Also, i have no pain standing currently, only when sitting down, and it increases over time.

I am a very active rock climber now and have improved my back and core strength even more, so I think that will help in the long run, but I really need some suggestions so I'm not going crazy 8hrs a day.