Original world wont load

So I have a world on minecraft, been on this one world for months maybe a year and spent alot of time and effort into making my world and all of a sudden, I login on 18 october 2020 and it looks like its gonna load then after a while of loading longer than usual it will say THERE WAS A PROBLEM LOADING YOUR WORLD  and I cannot get on it this will not load up but i try to make a new world and that works fine. Please can this be fixed as this has only just happened I got on ok the last time I was on the world but now I cannot go on it because the game wont let me.