Low hcg levels

Hey guys. According to my lmp and all my apps, I'm due March 3rd which would make me 6 weeks. I had an appointment yesterday and I had a vaginal ultrasound. The tech could only see the sac but no gestational sac and no fetal pole. My hcg levels were also only 1876. On June 27th they were 357. I'm trying to stay positive because I know it could possibly be too early to see something on an ultrasound but what has me so worried is the hcg levels because they are nowhere near doubling. I've had so many chemical pregnancies this year and last that I'm not sure I can take another. Has this ever happened to anyone and everything be ok? Sorry it's so long.