This sounds more like it my have root in the mind, rather then a physcial cause. If you go to see your doctor and he can't find anything wrong, then you may want to make an appoint with a psycologist.
See a doctor. It could be an allergy to medication. Or perhaps anxiety or nerves. You could have an allergy to something in your house. Or a vitamin deficiency.
The question is, are they really crawling on your body or not? If not,try to have a 20 minute warm shower and use sulfur soap to get rid off the germs that causing you to feel itchy most of the times.