Am I being unreasonable?

My ex and I have been divorced for almost 6 years. Our children are now 16, 14, and 12. In that time, I have paid for everything. I carry the insurance on our children as well as pay all the out of pocket expenses. Our divorce decree states that he is required to but he doesn't so I have to, so the doctors will continue to care for our children. I have even showed them the decree that states this but they all tell me its a civil matter and they can't get involved. They require payment so I would just have to get a lawyer to sue him for contempt which I don't have the money to do. I have paid for all the gles, contacts, braces, and medicines. Our youngest child has epilepsy pretty severe, takes medicine twice a day, and sees a specialist every 3 months, so this gets pretty expensive even with insurance. He is also supposed to pay a total of $396.00 a month in child support, which I rarely ever get. I haven't gotten a dime since March. I pay all the fees for athletics and buy all the shoes, equipment, etc. I also give each child $20.00 a week for school lunch which doesn't sound like alot but by the end of the month comes to over $200.00. I recognize they are my children and my responsibility, but they are also his. So today I asked him if he could help buy school clothes this year and he completely went off on me. He said that the only thing he was obligated to pay was the 396, (which after the lunches leaves me about 150 for all the other necessities like food, shelter, electricity). I feel like he should help pay. Starting school is a huge expense especially given that they have all grown so much. So am I wrong to think he should help pay for school clothes?