Expired mediation agreement, who has custody?

my ex and i had a mediation agreement, it expired in july, and we have not been back to mediation or court since. agreement was he has the kids mon-fri and i got them every weekend, teacher workdays, holidays, and the summer. as it is now, ive got my kids thurs-mon, teacher workdays, holidays, and handle all afterschool activities and doctor appointments. since the agreement is expired, and we have not extended it, is there anything to keep me filing for custody of my kids or are they still considered in his custody even though the agreements expired?

If you only have an agreement, regardless of whether the provisions expired, you can file an action for child custody.