Aww honey, I am so sorry you're going through this! *HUG* Just hang in there- you are doing what you need to do to make sure your child has every advantage they deserve and there is NOTHING to feel bad about. In a perfect world the dad would do this on his own just because he was responsible, but the world just isn't perfect, is it?
I know what it is like to have no money to spend and feel like your ex does! If his parents have money to fund his legal fees, chances are they have bailed him out his whole life and helped to make him the irresponsible person he is today.
You need to make sure your attorney is totally clear on what is going on and that your ex is trying to keep from paying the support he is supposed to by making it financially impossible for you to continue to pursue it.
Remember, family court judges- and attorneys- have seen EVERYTHING. There is nothing new under the sun to them and they know every trick in the book that parents on either side try and play. As long as you stick to your guns and have proof that your ex can afford to pay what he is supposed, it will work out in the end. You just have to hang in there, and I know how hard that is.
It sounds like your stress and worry is just becoming physical, but try to de-stress. Take a relaxing bath, have a cup of tea- whatever works for you. When you feel yourself start to get the shakes, just remind yourself that you are a GOOD MOTHER, and this is to help your precious child get what they need.
Picture yourself and your child one year from now. Maybe you have a better apartment, your child is in a better school. You have a better job and the support arrangements are all settled and automatically deposited and nothing to worry about. You are in a good place, safe and secure with enough money to take care of yourself and your child.
Just envision this, over and over in your head- write it down in a journal and read it out loud to yourself before you meet with your lawyer or go to court! Use that vision to help you stay calm and don't be intimidated!
Good luck- you can do it!