It shouldn't take long at all for the increase to take effect. Usually it's pretty immediate, since you've been on the medication already. It is NOT a matter of weeks! I would say that within a week, you should be feeling the total effects of the higher dose.
I just recently was switched from Cymbalta to Prozac, because the Cymbalta quit working. The Prozac began working IMMEDIATELY -- I felt wonderful the next day! And I'm very hard to medicate too, so I was very surprised!! He had put me on a low dose also, and I'd been on 120mg of cymbalta. I'm now on only 20mg of Prozac -- so this is pretty unusual.
I hope you feel better. Please take good care of yourself! God bless & take care. Hugs, Lee