My oxalic acid is high. Is it because of food? Do I need to follow a low oxalate diet?

No you don’t. I don’t recommend restrictive dieting anymore. They end up making cellular deficiencies worse in the long run. I've discovered this over time. 

And the amount of oxalates you get exogenously through your diet is so insignificant compared to the amount of oxalates produced endogenously within your body. So eating a low oxalate diet won’t make a significant difference anyway. 

Your oxalic acid is elevated not because of your diet or specific foods, but because your body is producing too much endogenously.

Being exposed to toxic mold also increases oxalate production.