minecraft crashes and mobs despawn

My Minecraft takes forever to load in (around 5+ minutes just to enter a world) and when it does it keeps crashing. Every time it crashes it causes me to lose my valuables, such as inventory or pets (dogs, cats, horses, parrots, sheep, etc. every mob gets erased from history, including villagers) 

it is very very annoying and it causes me to lose progress in my survival worlds