I had a tubal ligation 6 years ago, this paat month I was suffering from, really sore breasts frequent urination, lower back pain, and then I started heavy bleeding but it felt different from my regular periods, I went to a gyno and he did an ultrasound/sonogram and both pelvic and intravaginal, after exam prescribed birth control and naproxen, but still told me to take a pregnancy test rule out pregnancy, but,couldn't that be determined on a sonogram?

If it was very early in a pregnancy, a test will sometimes pick up a pregnancy before a definite determination can be made from ultrasound.