A bump is usually caused when you've banged against something. You get a bump on your head if you bang into the edge of a cupboard door. A lump is a bit that sticks out noticeably, but you've not bumped it. Like I had a little lump on my arm when a spider bit me. A swelling is more general and less obvious to see the edges. It's usually liquid-filled. Like if you have a swollen ankle. So I could have a bump on my ankle, if I've banged into something. I could have a lump on my ankle and I'd want to see a doctor. I might have bumped it and have a lump. Or I could have a swollen ankle after I've sprained it.

A lump is a piece or mass of indefinite size and shape. Example: She found a lump in her breast. A bump is a swelling of tissue. Example: He had a bump on his knee. A swelling is an inflammation of tissue. Example: The doctor advised his patient to use an ice pack to reduce the swelling on his cheek.