Is it a grass allergy

Hi everyone,

I have a Hungarian Vizsla dog, he is six and a half months old. Over the last three weeks he has been getting lumps on his back. It started like I said about three weeks ago, first there were only a few lumps around his shoulders these went down after a week and didn't seem to bother him much, not itchy or anything. Then I was out with him in some long grass and the following day I noticed a lot more of these lumps all over his back and some on his legs, more on the outer side of his leg. The lumps are hardish, round lumps no bigger than a centimetre in diameter. His chest and belly seemed not to be effected at all, no redness or lumps. I have taken him to the vet and he seems to agree with my observation and has put him on Prednisolone, it's a corticosteroid. These are known to have a side effect of excessive drinking and urinating, which my Vizsla has been experiencing almost straight away since starting this medication. I think that Steroids are a bit harsh for a puppy.
Have any Vizsla owners out there experienced these kind of lumps ? Could they be a grass allergy ? Are there any other ways to control this if this is the case ? I would be willing to try anything to get to the bottom of this aliment. I am considering Allergy testing, I know this is only really reliable for environmental allergies, Has anyone gone down this route and have you any advise ? Any help or advise is very much appreciated.