Are the test wrong or am i crazy ??

Unprotected sex July 26 , and again the following Monday 7 days later and he finished in me both times multiple times . I had my period on July 20-24 . Then on August 8th -12 I had light spotting very light started red then brown then pink the brown again . Which I didn't believe to my period because hadnt been a full month ,  and my periods are very regular very very regular!!!! i was late once but no longer than 4 days , but anyways my period was do August 20th ... And I am now 10 days late and took four first respon test all negative ??? am i pregnant ? Or should I be starting my period ? ??!! And I am a teen . The only symptoms I have had were lower back aches , and slight headaches every know and then cramping and pinching in my stomach .. ? And I want to get a blood test but if it's not even showing up on a test I don't wanna waist my time for a blood test to be negative as well ? Please help