Can you develop a tolerance to Cymbalta?

I haven’t been prescribed Cymbalta for depression and chronic migraines but it doesn’t seem to be working as well as it used to. Can you develop a tolerance to this medication? What should I do now? Thanks in advance.

What’s your dose? For me Cymbalta isn’t working full on as it should do I’m at the moment also taking Mirtazapine. 

Btw I’m on 60 mg.