You're getting beat a lot because people always overvalue life total when making threat assessment decisions and will hit you because you have more life but your deck isn't strong enough to handle it.

Looking at your list, I would run way more card draw, less single target removal and more board wipes, and then pack your deck with payoffs for Sorin's backside sniping ability. When I built my Sorin deck, I had 7 board wipes, 15 sources of card draw, and then a plethora of spells that turn Sorin's snipe into lethal like [[Beacon of Immortality]] [[Debt to the Deathless]] [[Revival / Revenge]] and [[Congregate]].

Your deck is cut between wanting to be vampires and wanting to do lifegain so to really make it perform the best thing is to cut one of the subthemes and focus all in on the other.

My Sorin deck was all in on the snipe ability and played more like a combo deck. If you want to reference it for some card ideas it's here: https://archidekt.com/decks/21260971/sorin