You don't give enough information for a proper answer. Where are these cracks? Pictures would be a big help. If they're on the belly, it sounds like chrysals, which are compression fractures. These are usually caused by one area of the limb doing more than its share of the work. In this case, the chrysals would all be in one small area of the limb. If they're spread over the whole limb, it probably means the design is wrong for that particular wood.
You might be able to fix it by removing the crushed wood and glueing a slat of new wood onto the belly and then retillering. I think when others chime in, they'll mostly tell you to start another bow. I have repaired a couple bows this way, and it worked, but doesn't look very nice.