Auggie is not feeling well

Auggie did not want to eat on Saturday morning and seemed a bit off the whole day. I took the boys out for a doodle romp in the afternoon and Auggie seemed to perk up and played with the other dogs just fine. I boiled some rice and chicken for him in the evening and he did eat some of it. Last night we heard him scratching constantly and at about 1pm my DH had to take him out because of loose bowels. I can smell bad gas coming out of Auggie on occasions this morning, he refused his breakfast again and is just moping around (although he did try to attack and chase Monty the first thing in the morning). But he is definitely not feeling well and I can't tell what's wrong. He is still scratching on occasions; I looked through his fur for flees, but did not see anything. I'm not sure if I'm imagining it or not, but it almost looks like his eyes are a bit swollen (just like mine since I did not get much sleep last night). I can't tell for sure. My DH said Auggie drank some water in the morning.

I'm going to the store to see if I can find some anti itch shampoo and give him a bath. Would you suggest a baby Benadryl or something? If so, how much? Any other ideas of what I can do before taking him to the vet tomorrow morning?