I have been bleeding really lightly a reddish brown blood for the past three days. There are very mild cramps but no clots or signs of my menstrual. Which is expected in 7 days. What could this be?

Brown blood is a sign of old blood and your body expressing it. It happens.

Are you sexually active? Is there a chance of pregnancy?

If so, wait for your next period. If you miss it, test using first morning urine a week after you miss it. If that test is negative you can test again a week later, or wait for you next period. If you miss it, test again, or see a doctor for a more accurate blood test.