how accurate are HPT

Jes
I'm TTC for baby number 2. I have some very suspicious symptoms at 13dpo. I tested negative at 11dpo and 12dpo. However I tested NEGATIVE my whole first trimester with my first born, I had to go get a blood test because I just knew something was off, I thought spotting was my period 
So I'm just wondering do some of us just not produce enough HCG in urine?  I wasn't TTC to conceive baby number 1 it was actually a nice surprise. 
Should I wait until like 20dpo to take a hpt or get a blood test?