Without a picture, it sounds like wilt and depending on where you live, Verticillium or Fusarium. Wilt flourishes in cool damp weather which we have had in the Mid-Atlantic. I have at least 3 plants infected by Verticillium wilt. There is nothing you can do except hope the plant survives long enough to produce fruit. The bad things is that this fungus lives in the soil for up to 3-4 years and there is no chemical treatment available to get rid of it. Solarization and crop rotation are the only solutions besides finding plants bread with resistance.

Thanks for the comeback but I already got an answer from another site. The problem was that I had "tomato stalk borers." Google it if you have an interest. I actually found one in another stem that was in the process of being eaten. There is no treatment other than to remove the affected stem and hope the larvae is still inside eating. Thanks again for the comeback Silverspring..