What's the best way to see my son?

I'm sorry to hear that. It sounds like you must not have an official written agreement or court order in place that gives you such rights because if you did, you would want to go to court for a violation or to otherwise enforce the agreement. If you only had a verbal arrangement or perhaps none at all, and she is no longer cooperating with you, you need to file a lawsuit for custody/visitation. You should consult an attorney right away to assist you with that. You can also look into some of the pro-se (do-it-yourself) custody forms that many counties have and which can often be used for any county so long as you change the county name at the top, but you should still contact an attorney to review those forms and other consulting before actually filing to make sure you are on the right path, etc.