You should hire a family law attorney and petition the court to modify custody. It is hard to determine based on the little facts you have given whether a judge will modify the custody agreement. However, a judge will take many factors into consideration when making a decision.
Custody is always subject to modification throughout the minority of the children. However, first you have to show that there has been a change in circumstances since the prior order, and second, you must show the court that the change you are advocating is in the best interest of the children. Courts tend to favor shared parenting, however, if you are serious about getting it done, you really should contact a family law attorney and do it right.
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Based on the brief description, you may want to focus on what has changed in the last 3 years. You must be able to show a change in the circumstance since the last time you signed your "papers". Ohio has a preference for shared parenting but will want to see evidence that your prior orders are no longer in the best interest of the children. This may sound simple, but custody cases are quite tricky to navigate without counsel and your question suggests that you may not have been provided all of your legal options the last time you were before the court. I would be happy to "flesh out" the issues in your case with a free consult (614)207-1673.
Disclaimer - I am a practicing attorney in Ohio. The law varies state to state. This is being offered as general legal education. There is no explicit or implicit offer to provide legal representation.