Yes I'd look to go down the Wikipedia reference-linkMRI route alright at this stage seeing as you've seen a physio and its not improving after 6 months. Another physio or doctor may be able to spot something after examining you that could mean not needing one but if your physio has looked at it already and didn't spot something the chances that another physio will are fairly slim.

One of the biggest problems with the sports medicine field is that it is hard enough for a practitioner to know how good another practitioner is in a certain area before getting treated by them, so imagine how hard it is for a lay person!

While the MRI may be costly depending on your situation, it should give you an idea of whats going on and be worth the expense in the long run.

Hope that helps.