i was playing my legacy sim and she got pregnant and had a child but for some reason the game isn't switching her from the maternity clothes into her normal clothes. does anyone know how i could fix this issue or is it just a EA problem ??

Have you tried having the sim go to the dresser, click on the dresser and choose plan outfit, to see if you can change the outfit in question?

i have and it says sim cannot do it because she is pregnant, when she isn't

OK, then that is where your issue is. Until you get the game to acknowledge that she isn't pregnant, you will have issues. Are you, perhaps, using Twallan's Master Controller or AwesomeMod? Both of these would be able to reset the sim and perhaps correct the glitch blocking you from having them move.