My girlfriend got a little spotting before a day of her expected periods..but till now she did not get her periods..before 15days we had a sex..but we didn't had penetration...and i wearing my jeanse ..i'm scared is she pregnant?

Pregnancy unlikely: A home urine pregnancy test (sold everywhere) gives a reliable result by 3 weeks after sexual activities (3 weeks after when conception might have occurred), or 1 week after missing a period, or 1 week after getting a "weird" 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.