Modification of Custody: Visitation Schedule Expired What Are My Rights

My question involves a child custody case from the State of: Illinois

My ex-wife has filed a motion to amend the visitation schedule set forth in the Joint Parenting Agreement that was agreed to in our divorce settlement. We had alternate week joint custody during the previous school year, and she is proposing that I would only get visitation every other weekend because she thinks that our son needs to stay in one home for stability. The visitation schedule that was set forth in the Joint Parenting Agreement stated that it was subject to review by both parties before our son starts school. I did not mind this because I understood that his schedule would change when school started, and he would no longer be using daycare services.

We have still not been able to reach an agreement on a visitation schedule for the coming school year when our son starts Kindegarten later this month. We have already been to a mediation session that did not produce any compromise or results. At this time, the court has appointed a Guardian ad Liteum for our son.

My reason for posting this matter here is that I need to know what my rights or legal standing are at this time for custody and visitation when school starts later this month. From my view, I would believe that without a court order or judgement saying so, that I would retain alternate week joint custody as we had before. Though the documentation states that the visitation schedule was 'subject to review', I do not take this to mean that my rights to have alternate week custody have 'expired'. My ex-wife believes that the arrangements set forth in the Joint Parenting Agreement are void, and that she can dictate that she will be keeping our son full time when school starts. Obviously, this is not acceptable to me.
Please let me know what the factuality of my rights are for custody and visitation. I would greatly appreciate your help. Thank You.