Answer: It sounds like tomato fruit worms. These pests are difficult to control because adult moths lay their eggs on the surface of the fruit and when the eggs hatch they burrow into the fruit and feed. About the only way to control these pests is to inspect the tomatoes on a daily basis and wipe off any eggs you see.
As for the blackened bottoms on your tomatoes, the problem is most likely blossom end rot. It is caused by a lack of calcium reaching the tip of the fruit. When the cells in tip of the tomato lack calcium during growth, they die and the black decay you see follows. You may have adequate calcium in the soil but still get this problem because of soil moisture fluctuations (from wet to dry). I have noticed that blossom end rot is worse on the first tomatoes of the season and tends to not affect later fruit as much. If you haven't had a soil test in the past few years, it would be a good idea to have one done to make sure your calcium levels are adequate. Your County Extension Office can assist you in having your soil tested. Blossom end rot is best prevented by keeping soil evenly moist. If your soil is sandy, and prone to moisture fluctuations, adding compost prior to planting may help. Garden centers sell a Blossom End Rot spray (contains calcium). This must be applied starting when tomatoes are about marble sized in order to prevent the problem. Mulching will also help keep soil moisture even.
Good luck with your garden!
Q&A Library Searching Tips