I'm pregnant and was bleeding on and off for 4 days have I had a misscarriage? Doctors say they can't tell as im under 12 weeks

Ultrasound, hCG test. There are some things that can be done in the first trimester to see if the pregnancy is miscarrying. One is to look for the size of the fetus and sac and the presence of a heart beat. Another is to perform a pelvic exam to evaluate for cause of bleeding, look at cervix, etc. Early in the pregnancy checking serial blood levels of HCG can be used to evaluate how the pregnancy is progressing.