Can I be forced to agree to change a prenup?

Before we married, my husband made me sign a prenup saying I wouldn’t ever claim alimony if we divorced. We’ve been married 6 years now and I have a very good job and am earning far more than my husband at this point. He now wants to go back and change the prenup to state that he has the right to alimony if we were to divorce. He says if I won’t agree to this change, he will take our son and move away with him and I won’t see him. I am afraid about this because he has been my son’s primary caretaker due to the amount of hours I work. Can my husband force me to change the prenuptial agreement? Do I have any rights if he were to move with my son and keep him from me?