Need answers

Okay so long story short I'm having every single symptom of pregnancy from Clockwork nausea to sore breasts Etc the doctor even expects me to be pregnant when I went there she gave me a urine test it was negative then she sent me for a blood test and it said my HCG level was more than one what I want to know is is there any other moms out there who have had kids in the past that their HCG level did not register in blood or urine with my first son they did not know I was pregnant until they gave me an ultrasound every blood and urine test was negative and with my daughter at two and a half almost three months pregnant with twins my HCG level was only 18 is there anyone out there who is like this that HCG does not register in their body I feel like I'm losing my mind I'm extremely tired all the time I get extremely nauseous at 10 every single night and it lasts a good six hours then I feel nauseous again in the morning by like 9 a.m. and it hits really really hard around 3 p.m. I've not had my period Going on 9 days now I need answers!!! The doctor will not do anything for me until I have a positive pregnancy test! Helllppp