Can diastasis recti cause pain in your upper left quadrant?

A repeat mri is not likely to show anything additional. Once you have imaging for an issue unless there is a change or it has been many years repeating the study doesn't show anything new.
Better would be to talk with a surgeon that does diastasis repair or abdominal wall reconstruction.
Things to consider additionally would be inflammation of the cartilage, pinched nerve etc.
Left upper quadrant pain would be a very uncommon symptom of diastasis directly. More likely some form of chronic use injury, old trauma etc. a good physical exam including nerves, ribs and a good history taking may provide some insight.

The most important thing was that you had an MRI to rule out something serious. Hard to know if it’s pain from the diastasis because it usually doesn’t cause pain. Could be a muscle strain but must also consider other non muscular things so you should continue to follow up with your doctor.

Diastasis recti is a splitting of the rectus abdominus muscles which can occur with pregnancy.  It is generally not painful but will cause a weakening of the anterior abdominal wall and laxity.  It is typically repaired in an abdominoplasty procedure.