However, I wouldn't want anything on medical records that might affect future employment
I should imagine an important factor would be the duration, rather than the severity, of your symptoms.
6 weeks duration usually marks the threshold between acute and chronic back pain.
As homonculus indicates, a decent clinician should be able to work out the difference between mechanical back pain and anything more sinister, ( eg cancer,
cauda equina ) through listening to your symptoms carefully.
MRI scans can be useful, although in the short term, justifying using public money on an expensive test, which is unlikely to add to the management of your care, may be difficult.
It's unlikely that it would be authorised by your GP, so you may well be in danger of going down the specialist route, which would, of course,medicalise your problem further.