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Presence of a brown discharge for a few days can actually be your periods. But just a single episode of brownish red discharge is actually confusing.
You should wait for atleast 1 week after the due date of your period to test for pregnancy. About 95% pregnancies are usually detectable by this time.
In case, you still have no periods and the tests are negative, you should consult your OBGYN doctor for proper evaluation and help.