Hi John,
I hope it doesn't sound like I'm nagging you, but you have to stop the self medicating with alcohol. It doesn't help in the long run and will only give you more problems over time. But please get medical supervision to help you quit. Depending on how long and how much you've been drinking, it could be quite dangerous to quit 'cold turkey'. Please speak to a Doctor about quitting, safely. Once dry/sober, you can then begin dealing with your trauma, with a trauma therapist, and with the help of medications if required. Dealing with your trauma is really the only long term solution to the flashbacks, insomnia and depression, but you can't work on your trauma whilst heavily using/abusing alcohol.
I also wanted to say that you have done really well to admit that you are drinking heavily, and to realise that it is leading you to fall into a bad situation - that takes guts and is the first step towards getting some help - so sincerely well done :)
You have made the first step by admitting there is a problem, now see your Doctor, and get the appropriate support.
Wishing you well
CB