Minecraft world reverts to new world removing all the work

Its done this before with me and my mates world as we created a world just for me to log back in ready to finish the cave we were haloing out just to fined that i spawned in the world spawn location and where we had built there was nothing and now with my private wold i created a enchanting table and searched how many materials i would need for 15 bookshelves and i pressed to join the world and it came up with world error and it spawned me next to  the cave you would spawn at if it was a new world even though the picture of the world is inside my house and my horse i want it back but i know that cant be done so i would appreciate if you fixed this bug as i don't think ill be playing minecraft by myself just to get major progress and for it to get deleted below is a picture i took showing that its real and im not lying