I had sex 11 days ago on 13/07/16, started my period today (3 days late) an it is a brown colour which is odd, am i pregnant? when shall i take a test

In 4 days: A home urine pregnancy test gives a reliable result 3 weeks after sex (3 weeks after when conception might have occurred), or 1 week after missing a period. If done sooner, a positive result is likely real, but a negative result may be due to testing too soon, and thus lead to a repeat test. If a woman gets her normal regular period, then she is not pregnant, and a test is not needed.