tubal? abnormal? too early?

My last period was December 13 through 18. I had a positive pregnancy test on January 11th. My first Dr appointment was January 16th. I would be roughly 4 weeks and 3 days the day of my appointment. My Dr came in the room and said I was 6 weeks ( dont know where he got that from) and then did a vaginal ultrasound. He began to tell me that he did not see the baby and it could be an abnormal or tubal pregnancy or just too early. I am now 6 weeks and feeling ok. Some symptoms are small cramps, bloated, gas, frequent urination, breast tenderness, and back pain. No bleeding. Should I be worried? Or was it just too early to see baby?