Am being treated for glaucoma. Dr is having a problem fitting me with contacts. My vision keeps changing & sometimes blurry. Why?

Dry eyes. Your symptoms are consistent with dry eyes. Fluctuating vision would certainly make fitting for contacts more difficult. There is no reason to assume that the dry eyes are related to the glaucoma. However, travatan can potentially exacerbate dry eyes.
Unrelated issues. Unless you had glaucoma surgery with some changes in the surface architecture of the cornea, then there is no relationship between glaucoma and the ability to wear a contact. Some glaucoma patients have eye dryness, occasionally as a consequence of the drops used to treat the glaucoma and this might explain difficulty in fitting a lens. But there are many lenses and one should eventually work.