Slow fetal growth, early pregnancy or miscarriage?

My LMP was on 15/3 which calculates that I'm estimated 9 weeks pregnant by now. First tested UPT positive on 13/4. Had some spotting at 4/5 hence went to the early pregnancy unit and have my scan done which shows a gestational sac and yolk sac but no fetal pole. Physician thinks that it might be early pregnancy estimated to be 4-5 weeks therefore no fetal pole was seen. Went for my next follow up on 19/5 and US scan showed increase in gestational size and a small query looking fetal pole of only 3mm. Yet again, not sure if the pregnancy is viable. Was told to wait another two weeks and go back for another re-scan which will then finalise the answer. Any advise? Or any similar experience?