Ouch man, thats some terrible luck. Hope it gets better, I just finished my W2 nuzlocke with only 4 casualties through out the game (one of them being a lilipup i caught in the second route, was a sad moment). I wish you luck in your endevour, platinum i would say is one of the toupher nuzlockes to beat, it along with firered/leafgreen are probably the two hardest.
But seriously, Platinum is a jerk for flinging crits all over the place. The only time your pokemon seem to deal them out is when you're trying to weaken a potential capture and then suddenly whoops, there goes your new party member for the route.
Beware EXP Share grinding as well... I lose half my team trying to strengthen up one new member after the second gym... so frustrating. My honest advice which I'm trying for my current run? Don't rush to fill up your party with pokemon. Just grind up 3 that is useful for the upcoming gym and maybe one from the last gym that you want to reuse down the line later.