Welcome to the forums.
Normally they try other drugs which stimulatr your insulin production (such as gliclazide) first, but if you've already tried those then it is normal. The metformin reduces your sugar production from the liver so it has a different effect to insulin.
Though that assumes you're in the UK and depends on what drugs your health system funds.... (New Zealand for instance is very stingy about funding drugs for T2 diabetics.)