Dog had an allergic reaction?

My puppy is 5 months and he had an allergic reaction to eating a spider or a bee outside on Friday. We rushed him to the vet and he got blood work and xrays and he told us that it was indeed an allergic reaction and gave him two shots, one that was to work immediately and one that would work for up to 4 days. He is feeling much better hes running and is happy, but he is more sleepy than usual and doesn't want to play as much. I'm just wondering if this is because of the second shot, I just worry about my lil guy, any answers would be appreciated.