urgent help- pregnancy fail? ivf

Worried... long rant but advice is needed, VERY MUCH

June 16 Beta 109- excited that we were preggers :)

June 19 Beta 275

June 21 Beta 524

At the times I asked if these were low numbers and they said they are just looking for increases in the numbers.  I was curious as mine seemed so low compared to other who have shared their's.  Then on the 21st after we reviewed the 524 they wanted to schedule an ultrasound for Monday, June 26th.  Today were are considered about 5 weeks and 4 days, close to 6 weeks.  This ultrasound was scheduled based on that there were no concerns just a check to see the measurements right?

Today, June 26th measured, Dr. G mentioned for the first time, your numbers seemed low so we wanted you to come in and make sure everything is there... (why was I not told this?  Maybe they are trying to keep it upbeat and positive I guess) During the ultrasound they did see a very, very, very small sack... Nothing else.  He mentioned that they sometimes happens when the body develops all the parts it needs for a pregnancy but there might be nothing in the sack.  Or the sack is there and the embryo is very small and not really developing like we would have hoped.  We were concerned then as I was worried our numbers from the betas were low but assured all was well.  I got emotional since these past 7 days we believed we were pregnant.  He wants us to return on Thursday, June 29th for another ultrasound, just to monitor and give this little embaby one more chance.  He said to continue to take the medicines as usual and Thursday we can discuss next steps.  Thank goodness we did not tell people, just our sisters.

This afternoon got a call, my beta is now 1833...  wtf!  The nurse asked me what Dr. G shared with me.  I shared with her all the above.  She mentioned she is glad we are coming in Thursday to be closely monitored again.  She said, "You are pregnant that for sure, this beta was a lot higher then before!"  She also mentioned the sack that was measured was measuring at less then 4 weeks... Good news it that everything is in the uterine cavity and not in my tubes.  Maybe they can try to get a heartbeat on Thursday, is what she mentioned.

Has anyone, please anyone had an experience like this?  Any hope?  Are our embryos slow?  Have there been successful pregnancies like this?  Would it have taken that long for implantation to occur?  Positive and reassuring comments are helpful, but if I need to hear reality I am ready to hear it...