I missed my period: it's been 12 days. period symptoms still persist and i experience fluttering in the lower left side of my stomach. took two pregnancy test and they were both negative. what's wrong with me?

Tests are accurate: Today's home pregnancy tests are very accurate and not affected by foods, herbs, common illnesses, sexually transmitted diseases, or medications. A home urine test will give a reliable result by 3 weeks after sex (3 weeks after possible conception) 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.