I suggest you have a few tests done. These include a Uroflowmetry, and an estimate of post void residue and an assessment of Serum Creatinine
. If these are abnormal, you might not derive benefit from drugs like Terol.
Depending on the flow and residue, we might have to start you on a system of self catheterization to reduce chances of kidney injury
due to high bladder pressures.
Also you should ensure that urinary infection has been controlled properly with appropriate antibiotics. The excessive urination alone is unlikely to cause dehydration