Considering your last menses to be on 2nd september, your baby should have been visible on ultrasound
In case it not seen other serious causes like ectopic pregnancy
has to be ruled out (pregnancy outside the uterus
Bleeding can occur in ectopic pregnancy and miscarriage
as well. But in your case the doctor has not seen any pregnancy in the uterus till now.
You should get blood beta hcG
levels to check if the levels fall in the discrimnatory zone for pregnancy to be visualized on ultrasound.
If yes ,You need to get a proper ultrasound from a radiology expert to confirm your pregnancy is intra uterine and viable.
Do not delay.
I hope I have answered your query.