Cymbalta working great first month then suddenly stops working?

I have been taking cymbalta for a little over a month (60 mg) and it had completely destroyed my GAD and have been working great. However this last week its been like it suddenly stopped working and I have had horrible anxiety and it feels terrible. Starting a new job next week so the timing cant be worse. My doc suggested bumping the dose up to 90 mg and have done so today. Is this normal for this abrupt stop in effectiveness?