Help with Slayer

Anyone else have a problem with what seems to be weak armor and weapons in slayer? I have watched alot of the matches I played in theater just to try and figure out why I die so easily and have a hard time killing other players. Some of it I saw was getting hit by two or more enemys but alot of the time it only takes a few shots with the assault rifle to take me from full shield and health to dead. Many times I would come up on an enemy that was engaged with another player so they should have had damage already then I unload a clip on them just to have them turn around shoot me a few times and Im dead. I have even seen it where I shoot up a player they kill me like swating a flie and while Im laying there I see them get hammered by another player and just keep on trucken like I didnt hurt them at all. I know there are tons of players that are better than I am it would just be nice to be on more of a even playing field. I set the matchmaking to find similary skilled players but it doesn’t matter. Do I have some settings set to low that Im not aware of? Any help would be appreciated.