Tips on latching

I've tried breastfeeding, I saw a lactation consultant but I'm not getting any results. I've been having to just pump. In the beginning he latched fine then all of a sudden stopped and he would only take the nipple or just wouldn't go on correctly. He did the ONE time the lady helped me. And he will occasionally take that side correctly but my other side he will rarely take at all (my bigger boob). How do you get them to latch correctly? I put his chin to boob and nose even with nipple but he still just doesn't latch correctly.