Three weeks late and need help!?

ok here's whats going on! I am officially three weeks ate for my period! I have always had a 31 day cycle even after I had my daughter in june two months later I was back to norma! but now i am 3 weeks late. i took four tests at one wk got one pos and three neg. so I went to a clinic they tested with a urine test got a neg. they wont do a blood test. could I still b pregnant or is there something wrong With me? who can I go to who will do a blood test?