I never received a positive while pregnant

I'm 5 weeks and still to this day can't get a positive on a test not even a blood test. They had to do a transvaginal ultrasound after I complained. My mom was pregnant with my little sister and she was testing negative on almost everything except vaginal ultrasound. My sister who is in the army was pregnant with twins and they told her she wasn't. Anyone experience this? I wonder is it hormonal issues