Hello and interesting question, hopefully I'll be able to help you out a bit. First of all, it would be very, very unusual to have any kind of hernia in this area, so I wouldn't worry about that at all. There are a couple of possibilities that I think it may be.
First of all, if the small bump is along one of the edges of the sternum, it could be what we would call a tender or "trigger point". These are very common in this area because this is where the pectoralis muscles attach, as well as where the ribs interact with the sternum. So this could be a possibility. These areas can also become inflamed when your back is irritated because the back end of the rib interacts with the spinal vertebrae, so if one end is out, it's likely the other could be as well. Either way, inflammation at the joint between the ribs and sternum is quite common and is called costochondritis. It's typically treated with nonsteroidal anti-inflammatory medications or ointments.
Secondly it could a small cyst, but that would be quite unusual, and probably not cause a great deal of issues.
I hope this helps, and it may be worth taking some nonsteroidal anti inflammatories such as motrin or ibuprofen, or if you have insurance there is also a new prescription gel called voltaren gel that works well.
I hope this helps, if not, let me know, best of luck...
Please ask if you need clarification/more information.
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Hello again, it's entirely possible that it could be costochondritis. Typically this is more of a localized pain along the sternum, but it can cause pain to radiate out to the side. It's also possible that it could be just what you're saying, a muscle cramp either due to muscle strain or caused by the irritated rib.
If it's happening on a regular basis it may be worth getting looked at, because it certainly doesn't sound like much fun. But if this is an occasional thing, some daily stretching of that area for a couple of weeks may be all that it takes to get rid of it.
Let me know if you have further questions...