He suggested applying pressure over my bladder when voiding. The common causes during pregnancy are kidney stones and compression from the enlarging uterus. The right side is most commonly affected during pregnancy. This is felt to be due the enlargement of the uterus. It does not occur on the left as often because the colon is in between the uterus and the ureter.
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.