I need help,my baby latches on the with most of the blackarea around the nipple in his mouth and yet?

i'm still getting a sore nipple all over again. He's now 4 wks and i had to take him off the for 2 wks and express along with formula all because of an extremely sore nipple and it's happening all again. also he sucks for so long at a time that i Have to be sitting or laying there with him for hours am wondering if he's getting enough which i think he is because when i squeeze the areola it squirts out. what am i doing wron here. i watch so many feeding video and i got the gist but something is just not working for me.