In order to be given full access to the forum you're going to need to post an intro, similar to this one:viewtopic.php?f=17&t=64327
Once you do that, you'll be able to post in the health section (you may be able to search it now for an answer to your question), ask the question there and get many more responses. A lot of the members don't really check out the intro forum and tons of our members are regulars in the health section.
We have had similar instances in our house, but it's a common occurrence for my girl Bailey. She's allergic to most things, and for the most part we're able to control her environment enough the occurrences have happened less and less. For us, our vet has advised us to give her Benadryl when we see these type of bumps (our girl's bumps and the one your boy is getting might be different-so be careful). And if they persist we take her in to see the vet. It can be from stress, or it can be from a mildly allergic reaction to something. Is there anything new in your dog's environment? Have you been away before?