Desk job back pain – new chair and stretches not helping?

I’ve had constant lower back pain for the last 2 months, definitely linked to sitting at my desk (IT job). Tried a fancy ergonomic chair and doing stretches from YouTube daily, but zero improvement. Pain is a dull ache, worse by the end of the day. Anyone found something that actually works for this? Should I push my GP for a scan (MRI?) or is that overkill? Physio waitlist is long.