7 weeks and no visible heartbeat during ultrasound

I am 7 wks, 5 days pregnant and just had my transvaginal ultrasound.  My physician wasn't able to detect a heart beat, but the the sac was visible at 5mm.  An HCG test the same day indicated that I am at 5700.  During week 4 my numbers were at 90, then at 270 during the next test.  My cycle length is anywhere between 38 days-60 days, although I conceived using femera (letrozole), so the cycle was typically around 32 days long.    

I go back in a week for a follow-up ultrasound.

My question is, could this be a miscarriage?  The doctor insinuated that this could be the case.  I miscarried during my first pregnancy, but at 4.5 weeks.  This seems much different and much later.    

I am growing more tired by the day, am having more food aversions and other pregnancy symptoms are increasing.  I'm just not sure how I could have absolutely no cramping or spotting and have lost the baby.  Should spotting be evident if the baby stoped developing early on?  

I am quite scared of going through this again and would appreciate any advice you may have.  

[remar]

What did your Dr say? Are you maybe not as far along as you thought?
You may want to post your question in the pregnancy forum because they will be better able to answer your question. Take care. Remar