My dog has a strange little red bump on his belly…?

So, a few days a ago, I noticed a red spot on his belly, I just ignored it. It wasn't painful to him, raised or anything. Just a little red spot.

Now, today, probably 3-4 days later, I noticed that same little spot is now a raised bump…?
It's the same size (about the size of a pencil eraser, maybe a little bigger) and it's bright pink…Not really red. It doesn't look inflammed/painful..
It's nothing like a cyst or tumor, if I even suspected that, he'd be at the vet.
It almost looks like a mosquito bite or a pimple..?
Except it's not really hard or real "bumpy," just raised off his skin. Not under the skin at all.

So…any ideas on what this is?
Should I take him to the vet?

He hasn't been acting strange and doesn't care when I touch the bump, it doesn't even phase him.

Advice..?
Thanks (:

Here's some pictures, sorry for the crap phone quality:

http://i158.photobucket0o0com/albums/t96/R…
http://i158.photobucket0o0com/albums/t96/R…