Why is my bathroom damp?

You need to fit a fan linked to the light switch so that damp air is removed regularly. Buy a good quality mould treatment solution and use it carefully following the instructions on the container exactly as they are often toxic. When you have removed all the mould redecorate your bathroom using a paint specifically for kitchens and bathrooms that is wipe clean and includes mould inhibitors. It would also be a good idea to remove the foam ceiling and replace it with a non-absorbent material.