Wow, and they say that the internet medical resource is a GOOD THING.
The internet, sadly, is not a pathology book. The only thing that'll come close is a doctor. Sounds to me like some kind of herniation of the intercostal muscles, but hey, I'm not a doctor either.
A mesothelioma, however, usually takes forever and a day to develop clinical symptoms -- on the range of 20 to 30 years. Also, mesotheliomas do not develop on the outside chest wall, but rather on the INSIDE, so the fact that you can feel a lump immediately makes me believe that it isn't a mesothelioma. Especially given the fact that chest wall pain very commonly mimicks pleuritic pain. If you could feel a lump in your pleura through an inch of densely-packed muscle and bone, you've got the most amazing sensory perception I've ever seen.
Blood in the stools can easily be hemorrhoids or something else that's extremely benign, especially if it is not a constant or even frequent thing.
Things the lump could be -- I've already mentioned herniation but that's more if the lump is between your ribs, and not directly on top of one. A lump directly on top of a rib could be a calcification from a tiny break there that you did not notice, a collection of scar tissue called a fibroma, It may be a bone cyst, another similar growth, whatever. A cancer you might want to rule out is bone cancer.
Bottom line -- go see your doctor, show it to your doctor, get him to take some x-rays (called rib x-rays series).