Thank you for the additional information.
It sounds like he needs further psychological treatment. Is there anyway he could talk to someone? You mentioned trying to get the the psychologist to call you back. It may be that he needs a new therapist, if the one he has is not following through with helping him. If it is possible, try finding him a new therapist. Ask his doctor for recommendations. Or you could check with your pastor if you attend church. Your pastor could speak with him as well to determine if he could help your husband.
If your husband will not help himself, it may be up to you to do what you can to help him. First, educate yourself as much as you can about PTSD and depression. You can search on line and books to get the information you need (I can recommend some books for you at the end of the answer). Also, talk with his doctor and therapist about what you can do.
If your husband sustained brain injury from the accident, he may have some emotional imbalances because of it. His doctor would know this and could talk to you about how this has affected him. You can also research brain injury and learn ways rehab therapists deal with this problem in helping patients recover.
Try just sitting with your husband without talking. Spend time in his company but don't ask him to converse. It can be a short period of time. It lets him know you care.
Ask your husband if he will go out with you just for a drive or to somewhere like a coffee shop. Try these outings a few times a week.
Tell your husband that you are there for him and that you want to help, but taking his feelings out on your son, or even you, is not acceptable. Then remind him of this when he does act out towards either of you.
Here are some books that can help you get started:
The PTSD Workbook: Simple, Effective Techniques for Overcoming Traumatic Stress Symptoms by Mary Beth Williams and Soili Poijula
The Post Traumatic Stress Disorder Relationship: How to Support Your Partner and Keep Your Relationship Healthy by Diane England
Shock Waves: A Practical Guide to Living with a Loved One's PTSD by Cynthia Orange
And do not forget to help yourself cope with the stress. Caring for a loved one who has gone through a trauma can be stressful and overwhelming. Do something for yourself as often as time allows. Get out and see friends, browse a bookstore, go to a park, or take a yoga class. Whatever you can do to help you deal with the stress and make it easier for you to cope.
Please let me know if you have further questions or want clarification.
I hope this has helped you,