What can I do if we're divorced and she still won't let me have my son?

You may certainly bring this matter back to the court that entered the order to enforce your parenting time. It is difficult to say from the limited information provided whether or not a judge would consider a change of primary care in your situation.

If you are really serious about enforcing your parental rights and your rights of parent time awarded to you in your divorce action, and you want to succeed in your efforts, that means you will all but certainly have to spend some money on an extremely good attorney. If there were a way for you to do this yourself successfully, I really wouldn't have any hesitation in telling you that you could. But the odds are against you. First, enforcing your rights to contact with your children is not something that most people can do if they are not experienced family lawyers. Second, even if you were to learn and know cold the law on enforcement of parental and visitation (which is now called parent time) rights in a divorce action, the sad and not so secret dirty little secret is that court commissioners and judges all but loathe people who represent themselves, particularly people who represent themselves in divorce actions, and even more particularly people who represent themselves in actions to enforce parent-time. I have seen people who are not lawyers but who areare well-prepared and to go into court seeking to enforce their parent time and doing an excellent job of arguing your case, only to lose because the court simply didn't pay attention to them and really take them seriously. So if you want to enforce your parent time, if you really mean it, then your best bet (there simply cannot be any guarantees in a situation like this) is to find the very, very best attorney you can and to fully cooperate with and to pay that attorney what he asks to do the necessary work. For most people, this means spending a lot of money they cannot easily spend. If you cannot reconcile yourself to that fact, there really isn't an alternative.

Move to have her held in contempt for violating the court's order. Judges don't like to have their orders ignored.

Yes. In fact you have her help in contempt for not following a a court order. The court might even give you custody as the parent most like;y to encourage a relationship with the other parent.

You need to file a motion to have her held in contempt, and prove that you came to get your child and were denied access (so she can't say that she waited for you and only left after you failed to show). You may be entitled to make up visitation for any that you were denied. If her conduct continues after she has been held in contempt, then you would be in a position to ask the court to modify custody and/or visitation. You definitely should consult with an attorney, as your motion will have specific legal requirements depending on your state or jurisdiction, and if you don't do it right you won't get the results you need to see your child.

There are two things you can do. File both a motion for contempt and a motion to modify placement. Most clerk of courts offices have basic paperwork you can use to file the motions.