Why do my ribs hurt all the time, suddenly?

About a month ago while I was playing football I suddenly got a real bad pain in my left side. The pain was in the area of my lower ribs. After that it gradually got better until it felt like it was going to go away, but it has lingered as a slight pain for about three weeks now. It also hurts in other areas around my ribs including the right side (which wasn’t the case originally). It hurts a little worse in the morning especially if I sleep on my side. The pain seems to be in the ribs, but conceivably it could be something else putting pressure on them.

The football game is a two-hand touch game and I don’t recall any contact of any kind happening prior to the pain starting (it was very early in the game). Prior to this pain developing, I had been playing three days a week for over six months, so it isn’t a matter of conditioning or being out of shape. Also, I’ve played football a couple times since it happened and, although it makes it difficult to play (breathing hard, reaching out with my arms, and running are painful), playing doesn’t seem to aggravate the condition any.

I’m really at a loss why this would suddenly start hurting for no apparent reason, almost go away, but then linger for such a long time.