Hello and thanks for posting. How long ago was he shot? Typically, we do not worry about lead toxicity unless t he pellets are actually ingested
can you elaborate on the red spots a bit more? Are they only on his tongue? no red spots on his gumline or on his abdomen?
do the spots look like open sores, or more like blistering? "red spots" is a bit non specific and as I obviously can't see your dog, it is going to be hard to suggest anything specific.
Certainly, with the appetite loss, I do think it warrants a vet check. A complete blood count can be done to see if he has an infection. A young pittie mix should be enthusiastic about eating, so the fact that hsi appetite is off is significant.
If you give me a little more detail, I may be able to offer more specific information. Given what I do know, I am going to recommend that you get your boy in for a checkup. Red spots can be small bleeds if there is a clotting disorder or a destruction of platelets (responsible for clotting) so I'd rather you err on the side of being aggressive and have your vet check him out. Best to you both. Kindly do click on accept as it is the only way that the site credits me- Dr. A