Firstly, thanks for your replies and advice, it's really appreciated.

I also think that 21 weeks seems too long for tendonitis, as I have completely rested (as regards the initial cause of the injury) and undertaken exactly what my physio has told me.

I am going to return to my doctor/GP and ask if I can be sent for an Wikipedia reference-linkMRI scan as the injury is obviously not clearing up as quickly as it should be

I'll post back my findings from the scan.

Thanks again