I agree with not using poas or dig or any other. The lines will not fade anyway on poas until a pregnancy is being lost (bleeding). Try and keep postive. Like pp said, if you are 6 weeks or so, then a heartbeat most of the time can not be seen yet.
The only way you could work it out is if you could remember what date you first saw a line on poas, then you would have been around 4 weeks then. Good luck. Lets hope in 2 weeks there is a nice heartbeat
Sending lots of positive vibes xxx