Pristiq 50 mg

I have been on pristiq 50 mg for 2 months and before that I did 25 mg of Pristiq for a month or a little longer. I suddenly have zero motivation, very tired and just feel blah. This happened in the last 2 to 3 weeks. They want me to increase to 100 mg. I'm hesitant to do this because I don't want to feel worse. Has anyone had this problem and increased and saw improvement??