Is my effective date safe for backpay?

TLDR on conditions, I dipped out of the service right before I was probably gonna catch a med board, because I didn't want to be in anymore, and it was killing my homelife. Anticipated 50% due to CPAP and SC sleep apnea. Even if the VA takes 2 years to finalize my claim, will it be backpaid to the day I applied? I'm also gonna run out of CPAP supplies I use because I don't have a way to pay for them right now... im in school full time and leveraging that to pay the normal life bills. Also, I want to use my move but I won't be able to purchase a house if my claim doesn't finalize because I won't be certain of income, and that just seems stupid to me, can anyone offer some advice on what to do moving forward?