Hcg levels ....

Kasondra • baby girl was born 11/21/16 💜 ttc for baby #2!
Please someone explain to me hcg levels I'm so worried and confused how can u be from 5-500 and still be ok ?? I just found out I was pregnant but my hcg level is only a 16 and I'm considered 4 weeks and 4 days or something like that so they keep telling me I'm just very early and have to retest tomorrow to see if they are doubling .... But I can't stop crying