Low hcg level

Holly

Hi I found out I’m pregnant last Monday my app says I’m currently 5weeks 2 days from last period

Lines aren’t really getting darker and clear blue digital still says 1-2 weeks

Went for bloods last Tuesday they was only 16hcg

And then went back for bloods on Thursday they went up to 28hcg I have more bloods tomorrow but I just feel like they are to low

Anyone experienced this