If my ex-husband has not abided by our divorce agreement, what are my rights?

A divorce agreement is essentially a contract; if one party does not abide by it, the other may sue to enforce it. That means that  you could sue him on the basis of the agreement to get  him to either literally do what it requires (called "specific performance") or else to pay equivalent monetary damages. You could sue yourself ("pro se") if you need to, but would be much better off getting an attorney to do so. If you can't afford a lawyer, you could try contacting you state legal aid (who provide  legal services to those who can't afford); your state or local bar associations (who might provide referal to an attorney who will do pro bono, or for free); or a divorced women's or mother's support or advocacy group, which may have some legal resources or recommendations to help you. Good luck.