My duaghter and I get COSTROCHONDRITIS all the time. You will need to be checked for infection, as that sometimes is the cause. We get it from having Lupus. Costrochondritis is inflammation of the ribs and/or sternum (mid breast bone) area. Bascially if you cough it will hurt, turn certain ways it will be sore, press on it sore, and it may be difficult to breath at times. Generally, infection is the cause but there could be other causes too. It is not an emergency but something to keep an eye on. The doctor will give you an anti-inflammatory like Motrin to reduce the swelling. It lasts about 2 weeks. If it doesn't resolve within 2 weeks you will want to get rechecked. See the doctor though, it is important that they have a record of the occurance and need to know what to look for if it worsens.
Also you may want a chest x-ray done just to make sure it hasn't affected the heart area as infections spread sometimes. Doesn't sound like it though as you would have symptoms similar to angina and it is rare to get Pericarditis/Endocarditis. As a precaution, if it does get weird and you have strange heart symptoms get to the E.R. pronto.
I hope this helps. Again, it is quite common to get this but a doctor has to examine you to be sure this is the cause.
Take care - Kristin