Can You Help On Puberty In Boys?

I think he's OK, this is normal for a boy in puberty.  If the soreness becomes intense enough that he is missing activities because if it then he may have a twisted testicle or some other problem that a doctor needs to look at.

Yes, it's common. It happened to me when i was around his age and my nipples were sore, firm, and all of these symptoms are normal. The doctor had told me. Make sure you tell him to check for abnormal lumps or anything that seems out of the ordinary. I'm not trying to be negative, but you don't want him to have anything tumorous. But the swelling of the testicles is normal in males going through puberty.

You're obviously doing a great job if your 12 year old can bring this to you. Tell him not to worry it sounds as though he is starting to enter puberty when his hormones (mainly testosterone) will cause some strange physical and mental sensations. (you may need to cut him some slack but don't let it become a cover all excuse!)
He may also value a little more privacy to investigate his developing body and he may also find he has wet dreams (spontaneous nocturnal ejaculations) he needs to know that this is all normal and happens to most boys at some time.
If he gets real pain in his testes get it checked out. Otherwise stay with it mum. Oh, and he should have a feel around his testes about one a month for any lumps or bumps. This is often neglected in education though we tend to tell girls about breast self examination. There are several web sites that cover this in more detail.

Thank you so much, I'm doing the best I can and both my sons, one is 17 and I are very close and they share everything even this personal. It has gotten better and I checked him the other day. His testes are a bit larger and now darker so my experience from my teenager makes me think that you are correct and it's puberty. His nipples aren't sore but I did warn him that may happen like his brother's did,..my oldest even had a lump under one nipple for awhile but it went away when he hit his first growth. My younger one knows  all about the "wet" dreams but hasn't experienced one yet.  
Thanks again for your input..forums like this sure help a single mom with sons out!