Very Dark Pregnancy Test.

Hi there! Anyone have any clue as to why my pregnancy test would be so dark before my period? I recently got rushed to emergency to rule out ectopic pregnancy, fortunately that was not the case and it was merely too early to see the sac on an ultrasound. My hcg level put my at 4weeks pregnant. And yet i had not missed my period yet. Ive taken about 6 tests now, all of which come back VERY positive. My boyfriend is a fraternal twin. Wondering if multiples couple be the reason for such accurate testing so early! Any advice or ideas from you lovely mothers and mothers to be ?:)