Is it possible to see a sack and a very tiny fetus at 4 weeks and 3 days on a regular ultrasound (not transvaginal)?

Possible. If u are not heavy, but u will need followup to make sure it is normal, u need a quant bhcg and a Progesterone level and another us at 6 1/2 weeks at that time should be able to see a small fetus with a htbeat.