Switching between windows PyQt designer - python-3.x

Question

I have been trying to develop a software in PyQt5.
I have 3 windows : 1) login
2) dashboard
3) appointments
Now I can navigate properly from login -> dashboard -> appointments perfectly.
But when I press pushbutton for back from appointments, it doesn't come back to dashboard.
But if I go from dashboard->appointments , the pushbutton works for 1 time.
I have removed irrelevant lines from the code to make analysis simpler.
login window class :
class Ui_MainWindow(object):
def setupUi(self, MainWindow):
self.MainWindow = MainWindow
def retranslateUi(self, MainWindow):
self.pushButton.clicked.connect(self.next)
def next(self):
ui = Ui_MainWindow2()
ui.setupUi(self.MainWindow)
self.MainWindow.show()
dashboard window class :
class Ui_MainWindow2(object):
def setupUi(self, MainWindow):
self.MainWindow = MainWindow
def retranslateUi(self, MainWindow):
self.pushButton.clicked.connect(self.next)
def next(self):
ui = Ui_MainWindow3()
ui.setupUi(self.MainWindow)
self.MainWindow.show()
appointment window class :
class Ui_MainWindow3(object):
def setupUi(self, MainWindow):
self.MainWindow = MainWindow
def retranslateUi(self, MainWindow):
self.pushButton.clicked.connect(self.back)
def back(self):
ui = Ui_MainWindow2()
ui.setupUi(self.MainWindow)
self.MainWindow.show()
Application starts from file login.py which has :
if __name__ == "__main__":
import sys
app = QtWidgets.QApplication(sys.argv)
MainWindow = QtWidgets.QMainWindow()
ui = Ui_MainWindow()
ui.setupUi(MainWindow)
MainWindow.show()
sys.exit(app.exec_())
The forward navigation always work, the backward one keeps failing...
Any help or suggestions will be very welcome...

Answer 1

Turns out I was writing the next or back function slightly differently than it should have been. The next and back functions should have been like this :
def next(self):
self.window = QtWidgets.QMainWindow()
self.ui = Ui_MainWindow2()
self.ui.setupUi(self.window)
self.oldWindow.hide()
self.window.show()
where self.oldWindow is the reference to the original window of the class enclosing the function next. This is also same for the back function.