Hcg level question...

So my baby boy will be 3months on Aug 5th.  I took a pregnancy test on July 20th which was positive, went to the doctor for confirmation,  they did blood work & my HCG levels were only at 31,  on Friday July 22nd, they were 79,  on Monday July 25th they were 170, & today it was 290.  Did anyone else have levels that were slow rising? I'm getting worried maybe this isn't going to stick with how the numbers are going.