Donna, first off a big hug to you from me.
What you are going through sounds so extremely difficult. Kudos to you for hanging in there and taking care of your kids. I've taught special needs kids in the past, and I know that
it is definitely not easy. I kudos any parent that deals 24/7 with their behaviour and challenges.
I think it is good to take a step back every now and then and see how far you have come and break what you have to deal with into chunks that are manageable for you. Some things we don't have control over, but the great things that you are doing for yourself, such as quitting smoking and pepsi are big accomplishments.
I know it is easy to revert back to old habits when we are stressed, but just keep your focus and goal in mind. We all have setbacks, so don't beat yourself up (as I often do), just take each day as it comes and do your best is all you can ask of yourself. Perhaps you can do something to ease the huge load placed on you? Seeing a counsellor is a first step. I used to be a counsellor for troubled teens, so I hope that some of what I said made sense. I always find that it is our struggles that make us stronger. Best of luck!