Is it normal to swallow your own sperm?

Not quite: It's normal to swallow one's own tears, as tears flow from the corner of the eye, into the tear duct to the nose, then into the throat. It's normal to swallow one's own nosebleed blood when lying down face-up, as blood flows to the back of the nose, and then into the throat. The penis is neither long enough nor connected to one's eyes, nose, or throat. Thus, swallowing is anatomically not normal.