HCG Levels possible ectopic??

Nona

So long story short, ER doctor told me I was having threatened miscarriage this past Sunday due to light bleeding, HCG of 133 at 5 weeks and no intrauterine sac noticed in transvaginal ultrasound. Went in for HCG every 48 hours since then and on Sunday they were 133. Tuesday 313 and today(I’m supposed to be 6 weeks) it’s 551. These numbers are extremely low. Does anyone have experience with this? Maybe an ectopic?