My MacBook has become very slow recently and not because of any software update. But it just became suddenly slow. Logging in to my account takes 2 minutes and even opening a terminal window takes a while to load. Apps take a while to open and quit. I even tried to reinstall macOS without formatting my drive but my MacBook is still as slow as a snail. Any ideas?

Thanks!

PS. I have 24GB left on my 120GB drive.

EDIT: I have a MacBook Pro (Retina, 13-inch, Early 2015) with 8GB ram. I am using this MacBook for 3 years.