Lump on Puppy's Face

I took my 5 1/2 month old puppy to puppy school on Saturday morning as usual and everything was fine. Later that day, I noticed a grape sized lump on her cheek. Kind of on her muzzle below her eye. It feels rather firm and I can move it around. It literally appeared in one day. It doesn't seem to bother her at all. I called my vet this morning and we decided to wait several days to see if it goes away on its own. Has anyone experienced anything like this? Thoughts on what it could be?

Could be from a bruise she got while playing, or a sting she got some time during the day. When Cole and Ember were puppies growing up together, we had lots of mysterious lumps. My best advice is not to play with it or check it frequently. hazel has been known to irritate lumps even more because she can't resist checking them...and the extra irritation tends to make them bigger :o

My puppy had a huge lump on her head, never knew what happened, vet checked it out. Think she might have bumped her head while playing as well. Keep an eye on it, and don't touch it.

My thoughts too. A bite from another puppy, a bump, a spider or other bug bite. Mine always have reacted rather dramatically, I mean in bump size, to the first mosquito bites, the first black fly bites, and the first deer fly bites, oh man, the deer fly bites are HUGE. Later bites seem not to affect them quite so badly. Even the first ones of the next season, a year later.