Hcg only increasing by 50% HELP

Hi all last Wednesday I passed quite a bit of brown mucous. I was seen by the early pregnancy unit on Thursday and Had a transvaginal ultrasound. I should have been 5w 1d but there was no gestational sac observed. My uterine lining was thick and the result was a pregnancy of unknown location. I had my beta HCG tested on Thursday it was 336 and Saturday it had only increased to 470. . Anyone have similar experience and what was the outcome, I'm not optimistic as we had a missed miscarriage at 8 weeks in February. Please help x