My period came 1 day late, and is usually right on time. its very light and mostly dark brown discharge with a little blood. could i be pregnant?

Possibly: This is either an unusual beginning to your cycle or an indication that your hormone balance has changed such as occurs with pregnancy, Be examined by your MD for the possibility of infection. If you do not start your usual cycle then you should perform a pregnancy test. Also a good question would be; are you at risk for pregnancy? This would make your concern more likely.