Whatever concerns your father has for you, it is never okay for a parent to do something like rummage through your things without your consent. It is never okay for ANYONE to do such a thing.
Yes, he is your father. He is entitled to feel concern over your life. But he is raising YOU, a fellow human being, a child, not training some monkey or cultivating a plant for stock. You are not a piece of clay for him to mold and manipulate to hid liking. That's not how parenting works. You are the one who gets to make the decisions in your life. The only one. And this breach of privacy, this micromanagement of your life, is not okay.
Information about almost every issue that you think you have to snoop for can probably be obtained by communicating with and listening to your child. But when you invade your child’s privacy, you communicate three things:
1. You do not respect their rights as an individual.
2. You do not trust them to navigate problems or seek help on their own.
3. You probably haven’t been listening to them.
It was a breach of your right to privacy for your father to snoop through your things. Why on earth would you want to share something with the kind of person who snoops through your things?
Your father needs to realize that it is not his place to violate your privacy, even if he does so out of concern or "because he loves you". That's not the point. You are a PERSON, and if he respected you, he wouldn't have violated your privacy instead of asking you about this like a normal person.
Talk about this with him. He needs to understand that what he's doing is wrong. He needs to know that this sort of behavior is not okay, and that if he expects you to trust him, he needs to trust you, as well. And if he would continue to do this sort of thing, be blunt: to continue to violate your privacy, he is violating your trust and the mental safety of having your own safe space, and he is giving you every reason to never trust him again.