For starts, no images done of your chest? (x-ray, CT)
It may be good to go to a doctor to rule out anything serious like a heart condition. However, I will sometimes get pain in my chest (on either side or both at once) from hunching over a computer or books, and it seems to be caused by sore, tight muscles. Try stretching your chest muscles by putting your hands over your head while standing and then leaning back slowly (it will probably start to hurt slightly worse while stretching until it gets loosened). Also stretch to either side. Alternatively, you could lay on your stomach, then put your arms next to you like you're are doing a push-up, then pushing up and arching your back to stretch, (like a "girl" push-up). Maybe try a heating pad. You could also use more ibuprofen (I find liquid Advil works well). If none of these work, then you should see a doctor. Goodluck!
It may be a good idea to see your physician to rule out any cardiac issues.
That being said, the pain could also be due to "Costochondritis" this is inflammation of the area between the ribs, and believe me, the pain can be unbearable at times and can also mimic heart pains. I have it and it hurts when it acts up!!!!
You say you have not been doing any strenouous work? Have you turned a certain way that could have caused this? Sat a certain way? It could be muscle related, such as spasms, I get those too, but in my upper back, but, they can spasm in front too, and again, it hurts. If you "google" muscle stretches, you will find some good ones to do and they are not that difficult.
While waiting to see your doctor, try putting a heating pad over the area and taking advil, for me, that is the only thing that works.
Good luck and take it easy.