Had sex last day of period(14th of oct)and numerous times since then.started period today but very light and no cramps neg test could i be pregnant.?

Yes...see MD: The pregnancy test measures the level of beta HCG (pregnancy hormone) which increases shortly after conception. Most urine pregnancy tests turn positive within 2 weeks after conception. A blood test is most accurate. It takes several days after conception for any pregnancy test to turn positive so a negative urine pregnancy test cannot be relied upon if you had unprotected sex one day earlier.