Unfortunately, your child support is not based on your net income. The only deductions from your gross income that are permitted are FICA, Medicare and NYC or Yonkers taxes. If you have arrears and are paying a pro rata portion of unreimbursed medical bills, then you are paying the correct amount although i cannot make a proper calculation without knowing Mom's pro rata share and the total amounts billed. Also, child care is a statutory add-on. In other words, you are required to pay your pro rata share of child care in order to allow the child's mother to work. That is in addition to paying direct child support.
I hope this helps.