I have been on 20mg of Prozac for nearly 5 weeks and I am suffering from some weird side effects this week. At first, it did a great job but now the anxiety is back. I haven't changed anything else about my lifestyle so I am sure it is the meds. I am having bad anxiety and I am VERY sore in my chest... like I have been lifting weights. Is this normal? I don't want to give this up because I know it takes at least 6 weeks and it has really helped my depression.