Yes, it is; Knot. And since you are covering your children now; if you were to bring the Contempt of Court action against your ex; you might be well served to request that the monthly amount that you pay be added to his monthly support obligation. I am not a lawyer, but I would suggest that you consult one to find out more about this. The attorney will be able to go over exactly what you are entitled to; and what the process entails to get your divorce (and your ex) back in line according to the court order.
One other thing; Knot. If you do not have an attorney, please consult with one. I understand many people do not want the hassle or expense of dealing with one in a divorce; but it really is a necessary expense. In your case, it is also one that you need only pay the retainer the attorney wants- your ex will be made to pay the rest. When the attorney gets all the orders on paper and filed; they will be enforcable- but not until.
I know of a woman (my neighbor; in fact) who thought she could do things the easy way. Her ex promised everything would be just peachy. Since nothing was officially a court order, she found out that she had no case when he stopped giving her money for her kids for awhile. She had to hire an attorney to learn the legal lesson: If it's not on paper, (and made an order of the court) it doesn't exist- and therefore not enforcable.