What are my options to revise my custody agreement for my 12 year old son?

My ex and I have shared parenting. The order states that I have him 7 days then he would have him the next 7 days and so on unless otherwise agreed upon.(We have an arrangement currently where he has him Sat evening through Wed morning and I have him Wed evening through Saturday afternoon) It also states that we will share expenses, and that we will both carry insurance on him. Over the past few years, I have encountered a lot of issues with him - he doesn't bring my child to school on time. This year, my son has been tardy to school 17 times - all on days that my ex takes him to school. He also doesn't pay for half of everything - when I ask him, he will tell me he doesn't have the money etc. I keep a running log of when I've asked him for money and he doesn't pay. He currently does not have insurance on him either. He does not pay child support bc I waived initially thinking we would split expensnes.