co parenting

Hi ladies,
i left my ex in January we have a 2 year old child and due to circumstances my son and i moved 4 hours away from his dad, his father sees him every second weekend for 3 nights and is able to have a solid week with him 4 times a year. Our relationship was abusive in every form. and now were trying to co parent but he is still trying to control our lives. he took my son to have his hearing checked (i have no problem with this) after i had taken him to my gp about his hearing and my gp said he was fine, to take away his dummy. when my ex took my son to the hearing place my son was sick, he had a head cold and was prescribed antibiotics the day before. his hearing test came back that he had some troubles hearing low frequencies, my ex is now fighting with me over getting his hearing rechecked now that hes better. hes also pushing to have him go through the private system if he requires surgery. i have no problems if he needs to be in public or private as long as the problem is fixed asap. How do i co parent with my ex when i feel like im co parenting with him his girlfriend and his mother? hes never cared about private heaalth before (got cranky when i wanted it and refused) but now his girlfriend is paying for it hes all for it. i dont know im just really stressed.