It sounds like you are depressed. Do you do any activities? Go out with friends or family? Do you take any medications? You may want to talk to your doctor. Don't be embarrassed. It 's better to find the answer then ignore it.
Losing interest in ones hygiene standards can be a sign of depression.
Keep a note to see if there are any other changes, like losing interest in a hobby, for example.
Do you have any other problems with your body, like stiffness or pain due to arthritis? These types of things can also stop you from wanting to have a regular bath/shower because of problems and the discomfort getting in and out of the bath. If that is the case, there are all sorts of bath aids available, like stools, grab rails and so on.
Could be due to depression. I would suggest forcing yourself to take the bath, no matter how you may not want to, this is the only way to break this cycle.
This sounds like a form of OCD or other psychological disorder which could possibly be treated with medication. There are other forms of behavior like this, such as pulling one's hair out constantly. They are true medical disorders which a psychiatrist may be best suited to help you with. You probably won't be started on anything until you can make an office visit, however. :)