This might sound crazy but I swear it is the truth
I once had a mix maltese that had that problem.
She was allergic to grass.
She had to get shots every month..this was 15 yrs ago
At that time I could not afford dog shots every month.
I tried keeping her inside but, it did not work because we would carry grass and dirt in our shoes..I thought I was going to have to
BUT..
Someone took her in gave her the shots and as far as I know is healthy and beautiful .