Go to the doctor and have them take a look. Could be an infection and you want that cleared up as soon as possible.
I would ask a doc but sometimes baby pushes against bladder and then once your bladder is empty baby will shift to fill extra space that might be the cause of pain
Sounds like a bladder infection. It's common in pregnancy. Drink cranberry juice and call your Dr. They may want to give you some antibiotics to clear it up.