Very dark line on pregnancy

Hi am pregnant with my 4th child but am in need of some advice.. i did a pregnancy test on December 26th witch made me 4days late on a period the positive line appeared fast and so dark. I’ve booked in with a midwife who worked out i am around 4 weeks pregnant. With my other 3children i found out around the 2 week 4 week mark and all them positive test line was so weak so how at 4 weeks are they coming out so dark now anyone else experienced this? Love to hear all your opinions