Questions about owed back support

I owe over 18000.00 back support partly because i was 14 when i had my daughter and partly because of sesonal work. i am paying my current order even though we are spliting custody of the child she lives 6 months with me and 6 months with her mother.also i help her mother out as much as possible ie i buy all her school clothes and supplies i also pay half of her extra cirricular activites.. ie cheerleading softball basket ball.

Her mother is now threating to put me in jail for the back that is owed.. is this possible being that i am paying my current order and that i have my daughter the same amount of time that she does? also about 2 months ago she dropped my daughter off with out even telling her saying that she couldnt handle her ans was stressed.. so we had her for a month then her mom came back and now we split the time evenly.. just need some answers..
thank you