Hi - welcome to YT and congrats
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It's not normal that he spent 2 days screaming after his shot - did you follow up w/ the vet? While some soreness from a shot is normal (just like for us), really bad pain is not normal. If it's still tender - I'd really get in ASAP as it could be an abscess.
You can groom at home any time, that's what I do as I think it's much safer than a groomer. If you want to use a groomer, then you need to wait until he is fully vaccinated.
I would keep a close eye on the spitting up thing...hopefully he will grow out of this. If he doesn't, I'd try a different food...