Pregnant women do get kidney stones. Since your hydronephrosis was associated with flank pain and x-rays are minimized in the first trimester of pregnancy, a stent was a reasonable thing to do. Stent pain and bladder irritation can occur and the degree varies from patient to patient. Since no stone was found it might be worthwhile to consider removing the stent with the knowledge that the flank pain could reoccur. Your bladder problems are most likely related to the stent and will likely resolve after pregnancy.
Patients often have variable post void residual volumes of urine in the bladder.
350cc is elevated but this may have been due to the ditropan. Now that you are not taking this medication anymore, things may resolve spontaneously. Your incontinence is almost certainly due to the stent and the resultant bladder irritation. It is important to realize that bladder infection during pregnancy puts you at risk for preterm labor. Everything done to this point has been appropriate.