Custody Modification in Iowa: Advice truly appreciated!

Current custody agreement is 50/50 joint with no child support ordered to either parent. The agreement states that parents may create own schedule of where child stays and when but that if an agreement cannot be made we will revert to alternating every other week. However for past 2 years, child has stayed with me for a modest estimate of 215 days of the year (weekends with father only). He has her covered by HAWK-I and pays $10/mo. Currently our child is having medical issues and requires treatment that he doesn't always support. She has learning disorders that affect her in both school and at home. I would like to know if it is possible, due to her father not being her primary caregiver or even joint caregiver, anymore; to modify current custody order so that I have authority to decide medical/legal/etc AND to begin to collect child support. Thank you so much!