HI, I'd like to help you with your question.
Yes, it is completely normal for you to experience these symptoms given the nature of your career experiences and what you have seen. You do have symptoms of PTSD. Since you are aware of having PTSD, that is a good first step. Educating your self is also important. The more you know about what you are dealing with, the better you can help yourself heal. However, you need to do more to help yourself deal with the PTSD.
As you probably already know, you have having typical symptoms for someone who has seen a lot of trauma. Although self help is great and very effective, in order to help you deal with how you feel, you need to seek out therapy as well. Therapy can help you desensitize from the trauma and give you ways to cope with the other symptoms. It also gives you support, which you need to help you through. The Marines, through the VA, should have therapists that specialize in PTSD symptoms. Law Enforcement may also have staff available for you as well. You can contact either for help. Therapy techniques to deal with PTSD have come a long way and are gaining more and more ground in helping those suffering with PTSD.
Also, you may want to consider attending group therapy. Sharing your experiences with others who have been through the same kinds of traumas can help you feel less alone and give you avenues to work out your stress. This is not easy to do for some people, but the benefits are worth it.
If you attend church, you can also talk with your pastor. Faith can play a big part in recovery, giving you a place of sanctuary and comfort.
Support is the most important part of helping your recover. Try surrounding yourself with friends and family who understand what you are experiencing. When you have a bad time of it, lean on them for support.
A couple of resources that may help:
http://www.nimh.nih.gov/media/video/tuma.shtml. This is a current article regarding help for those who experience PTSD through their experiences in the military. Many advances have been made in treatment to help military personnel.
Also, a book called The PTSD Workbook: Simple, Effective Techniques for Overcoming Traumatic Stress Symptoms by Mary Beth Williams and Soili Poijula is very helpful.
There are many resources to help you get through this time and learn to deal with the trauma of war and of police work. Reach out and let others help you recover.
I hope this has helped you,