Beta test help!!

I’m really worried n I just can’t shake this feelings. I have been ttc almost 3 yrs n this is the firs time I saw a +. My first iui failed, I am on my second and current iui. I am about 5 weeks on my 4th week I had a sharp pain thts when I found out I am pregnant they did a beta test n it was 74.65, the ultrasound shows nothing. A week after I had to redo my beta test it was 485.60 it should have been 597 my doc say it’s not raising as it should n tht I would come in nxt week to redo one. They say if I get any spotting n pain I should go in. On Saturday I got one drop of blood so I called today n they say if I want to go in I can as I also have cramps or if I want to wait n c. I told them I will wait. My thing is how far apart should they do a beta test isn’t one week after too long? Today is 3 day since my last test I’m 5weeks5days. If I go in should they c anything on the ultrasound or is it too early?