Prozac is used off-label to treat PTSD or it's symptoms, it's actually more for OCD and bulimia. I was prescribed during hospitalization but it did nothing for me, and nothing after my pregnancy either. Things really didn't look up until I got on zoloft and seroquel. I would talk to your doc, prozac isn't really great for ptsd. It had more of just a placebo effect on me. Here's a list of the drugs mainly used in PTSD treatment. most people with ptsd if on prozac take an average of 40mg+.
http://www.drugs.com/condition/post-traumatic-stress-disorder.html?sort=rating&order=asc
and here's a quote on zoloft if your interested.
"Posttraumatic stress disorder
Two double-blind placebo-controlled studies confirmed the efficacy of sertraline for severe chronic PTSD in civilians, with the mean duration of the illness more than ten years. Physical or sexual assault was the traumatic event for more than 60% of the subjects, and 75% of them were women. Over the 12-week period, 53–60% of the patients treated with sertraline were much or very much improved vs. 32–38% for placebo.[6][82] The treatment was continued for another year with some participants from both trials. The condition of the responders further improved; some of the patients who did not respond to the initial 12-week trial slowly improved as well, so that about half of them were classified as responders by the end of the following 24 weeks. The authors noted that the medication worked more slowly for those with more severe symptoms.[83][84] Discontinuation of the successful treatment after six months resulted in the return of the PTSD symptoms in 52% of the patients vs. 16% in those who continued taking sertraline.[85] Longer-term treatment has been advocated in such cases.[84]
Three-way (placebo–sertraline–third antidepressant) comparison trials of sertraline for PTSD found it to be better than placebo and equivalent to venlafaxine (Effexor)[86] or citalopram (Celexa),[87] and in a two-way comparison it had the same efficacy as nefazodone (Serzone).[88] Sertraline was not effective for veterans with combat-related PTSD.[89][90]"
I don't know the details though and I am not a pharmacist or a psychiatrist so take what I say with a grain of salt, and merely consider what I'm telling you as here-say by my T. He's a great guy though, he explains everything and specializes in preventive care.