Forced to stay in old hotel, room smells moldy. I'm sensitive to mold. What can I do? Changed room.

Leave hotel. If you're sensitive to mold, there is nothing you can do but avoid it at this point. Going forward, you may well be a candidate for desensitization shots from an allergist, but that won't help you now. If you have to stay where you are, the best you can do is treat symptoms until you leave.
Room/hotel change. Hopefully a new room in the hotel will be mold free. If not or you are very sensitive, then it depends upon the definition being forced. Because the alternative would be to find another hotel. With no choice, take an anti-histamine like Benadryl or Chlorpheneramine before you re-enter the room.
Light, heat, air. Sounds like a chapter out of worst case scenario - stuck in a moldy room but can't leave - what can you do? Open the windows to dilute out the mold-filled air with fresh air. Leave a light on in the closet with door closed to dry out the closet. Turn heat up in room to dry out room. If stuck there many days clean walls with diluted bleach or lysol spray. Pull furniture & drapes away from walls.