Will I get in trouble for posting nude photos of my ex in a website?

Of course, you will get in trouble! The possibilities range from a civil suit brought against you by your ex to criminal charges by the police, especially if the photos were taken when she was still a minor. It doesn't matter who took the photo or if she agreed to pose for it; if you posted the photos, you will be liable for any result of that posting. And if you did it intentionally to hurt her or cause her harm, the fines and prison time are going to increase dramatically.