How am I able to know that someone performed witchcraft on me?

You got a large wart on the end of your nose and an affinity for cats and pointy hats.

Ask them?

A white witch would not have cast a spell on you without your permission. Period.

What makes you think someone cast a spell on you?

Yes, can we hear the reasons/circumstances that make you believe something spiritual is afoot? Can't help without further info.