You’ve had a very tough up-bringing. There is no shame in having difficulty dealing with it. What you are reporting is not unusual for a kid who has witnessed violence and been bullied.
I really think you need to see a counselor. A caring counselor can help you learn how to manage the flashbacks and can teach you kinder ways to cope when you are feeling over-whelmed.
If you think your parents won’t listen to a request for counseling, you could ask another adult you trust to intercede for you. You might confide in your school guidance counselor or a teacher you trust or your doctor. That person could then help you talk to your folks.
In the meantime, when you are feeling down or scared or suicidal, please contact a counselor at the Boys Town Hotline. (Yes, they talk to girls too.) The number is 1-800-448-3000. Counselors are there 24/7 to provide help and support to teens like you. There is no charge for this service. Here’s their website: http://www.boystown.org/hotline.
I wish you well.