When you say that someone made a video out of your photos, do you mean on your phone itself? If not, how did you see the video?
You didn't mention what type of device you have, but Android has a feature in the Photos app called "Collections." This feature automatically groups together a series of photos from a trip or event into a slideshow/movie. Is it possible that you stumbled across this feature in your Photos app?
If you think someone was able to access your phone, you should change your password (Google password if Android, AppleID if iOS) immediately. I strongly suggest using 2-factor authentication for greater security, and of course if you aren't using a screen lock, anyone who picks up your phone would have access to your personal information and data, so start using a screen lock if you aren't already.
can automatically upload photos and videos taken on your phone to cloud storage.