What Breed Is My Dog?

We were told he was a Pit Bull/Husky mix when we got him, from a girl who could no longer take care of him. At one and a half he is pretty massive. He weights 70 lbs. and is the sweetest, most loving, cute dog you could ever meet. He drools everywhere, has huge lips that hang over, sheds quite a bit, but not too badly, he's pretty lazy, but can also be very active. After taking him to the vet the other day they told me he looks like a Lab/St. Bernard mix. His skin is spotted like a Pit Bull though, so I'm really confused at what he is. I do see St. Bernard though! Please help.