Re: I am in a dark place and end of my rope
Listen you sound like a very caring mom to your children. You would strongly benefit from some kind of support group where you could go and talk out these problems and feelings. But first you need some respite care for your kids so you can get out in the evenings. Contact your county board of developmental disabilities office and say you want to speak with the Intake Office about getting respite care services and even a big brother role model for your son. Also whatever services might be available, even some counselling for you and your daughter and your son.
Then ask around if there is an autism support group close to where you live and make arrangments to be able to attend the once a month meetings - ask your older children to help out with your kids until you get some respite.
You need some time to yourself. Don't your younger children go to school? You could use their school time as a time to perhaps get a part time job for yourself or do some things that are fun and enjoyable just for you. Respite care would give you some time to take your daughter out, just the two of you.
Try to take some breaths before you yell and know it's only to make you feel guilty. You do love and care for your kids but you need to start reaching out to your county for some services. Good luck to you.