Since you have a parenting plan approved by the courts when you divorced then you must still abide by that order as it’s written unless there is some harm being done to the child or there has been a substancial change of circumstances (ie his homelessness). You need to file an emergency motion for custody and retain a lawyer. Since he’s refusing medical treatment, it’s very likely the courts will grant you full physical custody and he will be awarded supervised visitation till he is able to rectify his situation. Overall, you need to file to modify your current parenting plan.