The time to ask for it is past. You should have been asking for a child support award retroactive to January. Did you do so? If so and it was ordered that mom pay you child support from January then you would have overpaid her from January to June and could file. Please clarify the situation.
Parents should remember 3 things: Love your kids more than you hate your ex; when you have children the relationship with the other parent is until death; your children determine what type of nursing home you end up in.
Nothing stated by me should be taken as giving you legal advice or forming an attorney/client relationship.
Attorney-GAL in Ohio.
I've removed the knife from my back, polished it, and will one day return it -- long after you think I have forgotten.