Period only lasted for 1 day! Has it ever happened to you? What was your experience?

Usually my period is regular and it lasts about 3-4 days. This time, I had pain on my left side so I figured my period was coming but it only lasted one day! I filled 2 pads with bright red blood but then nothing after that. for the next two days I saw brown when I wiped. Could I be pregnant? I am planning on taking a test this week but I'm freaking out