We found a bump too! On my new puppy she had shot done exactly a week ago today and just found a bump under her skin yesterday. We rusher her to the vet and they said it looks like a delayed allergic reaction. and just to put moist heat compress and rub it...
Went home and found this web site
New Puppy
VACCINE REACTION
There is a less than 5% chance that your puppy may have an allergic reaction to something in the vaccines. One type of reaction is the "flat puppy syndrome". This is where your puppy collapses, usually within 5-15 minutes of the injection. This type of reaction is considered an emergency however, it rarely occurs. The more common type of reaction (still less than 5% of the time) is where the eyes, lips, nose, and face swell up, or he gets lumps/hives all over his body. This can happen within 15-30 minutes, 2-3 hours, or 6-8 hours later. Treatment for this involves an injection from the veterinarian or the administration of oral benadryl.
A third type of reaction is a delayed reaction where the pet gets a lump under the skin where the injection was administered. This will come up 1-3 weeks from the time of vaccination and usually goes away within 1-2 weeks. Because the vaccines will change each visit during the puppy series, look for these allergic reactions each time your puppy is vaccinated.