HCG levels

embee
My husband and I have been TTC for over a year and have suffered 2 miscarriages. I am currently 5 weeks 2 days and have been getting my hcg levels checked. 
First check was 18 dpo = 669
​48 hours later = 1148
​72 hours after that (today) 1928
​It's not doubling and I'm starting to freak out. My levels were never checked before so idk how they looked at all with the previous miscarriages. I'm having another draw on Friday followed by an ultrasound. I know we're not going to see anything this early which doesn't help but they want to make sure the pregnancy is in the right place. Has anyone had experience with levels like these and what was your outcome? 
​Thanks x