Hi, I Had Been On Venlafaxine150 Mg For About 3

Hi, I had been on venlafaxine150 mg for about 3 to 4 months but had to change because of bad constipation and night sweats. I just started taking Prozac 5 days ago. I know that it takes as much as 6 to 8 weeks s to feel the effects (20 mg) but after 5 days I don't feel right. I feel anxious, headhachey behind the eyes and down depressed. I know it's to soon to feel effects but could the two drugs in my system be causing what I feel?