PLEASE HELP!!!!

Charlie • Hi everyone! Trying to conceive baby number one.
Hi, im late for my period by 3 days and im 15dpo, for the last four days ive been taking tests, 3 different brands and their all showing possitive but the test line is very faint, its noticable but shouldnt it be getting darker by the day rather the staying the same? I was excited but now im concerned:(
​Thank you!