Dogs Eyes & Face swollen?

We have left a message for our vet and are awaiting a callback now.

I am suspecting an allergic reaction, but figured I would see if there are any other suggestions.

I have a rescued beagle-jack russell mix that when we woke up this morning we found that his whole face - around his eyes and his snout - are swollen.

He only goes outside with someone for walks, he normally sleeps with my husband & I but chose to go into his crate sometime in the early morning (3-4am).

It is perfectly normal for him to need to go out during the night, but he did want to go out more than normal last night -- which happens every so often -- he was eating alot of grass when I took him out, he did throw up once. Again, he does this every so often so it was not completely out of sorts.

I've looked in my books & online and an allergic reaction is the prime suspect here. But does anyone else have any thoughts/ideas? He is not lethargic. He has eaten his breakfast and has drank water. He has gone potty normally. His face is just swollen and we are concerned.

Thanks,