Low HCG level, posible Ectopic Pregnancy...

Hello, I received a positive pregnancy test 8/20 might be 6-7 weeks by now. I’ve been monitoring my HCG levels since 8/24. Am getting really scared they’re not doubling. They’re going up slowly which can lead to an Ectopic pregnancy. Has anyone heard of something similar to my situation? Am starting to freak out if it’s an Ectopic pregnancy and my Fallopian tube can rupture. Trying to stay positive and hoping it’s just an early pregnancy and miss calculated but don’t know what else to think. Also, did an ultra sound but didn’t see anything. My next follow up appointment is in two days, seems like forever! Any advice or guidance?