I don't think you started on milk too early doll, some say carry on for a few days , some say go to milk, I tend to if they're a bit weaker I put a bit of colostrum in milk, but very rarely. I do think that one lamb can be to date in a ewe from first raddle mark, she couldtake for the second so called twin later, so then ou could have one spot on lamb and one that s come out and not quite cooked yet, if that makes any sense at all. This little lamb probably was a little underdeveloped, lungs not strong enough. Not enough body fat. Keep going, it won't always be like this. Xx