I am smelling and tasting crack smoke, after six weeks clean.

What you describe is a form of craving.  Craving is insidious and can take a lot of forms from having a desire to socialize with friends who have used drugs to even dreaming about drugs.  In your case, you have craving in the form of olfactory and taste memory.  I can't tell you why your craving is taking this form, but it is reasonable that after only six weeks that you would have some form of drug craving.  What you need to do is, that when this happens you should recognize these sensations as craving and be particularly careful about your actions so as to avoid relapse.  If you are in an AA based program, it is a good time to chat with your sponsor.  Over time I expect that this is going to get better.