my pregnancy test arent getting any darker?

Brittney • Mom of 4 & Wife ❤️ #pregnantwithtwins

I got my bfp at 10dpo.. today is 12dpo and they still look the same on the cheap pregnancy strips... my lines are still a faint positive but are noticeable, I've took 3 types of test and they all came out faint Positive, but I thought each day your hcg levels were suppose to go up.. I don't start my period for 2 more days... when will my test start getting darker ??