Wa'alaikumassalam! Ya, it's pretty normal at 30 weeks, your uterus is pushing up on your diaphragm so breathing feels harder, especially when you lie down flat or do simple things like climbing stairs. A few of us mummies found that sleeping with extra pillows to prop ourselves up helps a lot, and taking things slower really makes a difference (macam don't rush when walking or doing chores la). That said, if you're getting really breathless doing nothing or feeling chest pain, better check with your doctor just to be safe, okay?