I've been told before that Prozac is the most activating of the SSRI's, and 20mg is still a low dose. You may feel very different on a higher one and I think a lot of Psychiatrists would give a drug a full trial before adding more.

I think I went up to 30mg Prozac and I had terrible, terrible restlessness. Legs never stopped shaking.

I've also have had my history with Remeron and, I hate to break it to you, but that thing is extremely sedating. Consciousness destroying sedating. Higher doses there is a chance for the sedation to go away and even become activating, but for the lower doses it's an incredible cure for insomnia.