Passing out at the mall

Today I was shopping with my friend and went to go pay for some clothes well out of literally no where I got super dizzy super hot and the room started spinning and I ended up blacking out and passing out . I had enough time from feeling like I was going to pass out to actually passing out where I was able to tell my friend I didn’t feel right and she was able to catch me so me and baby are fine (: I am 15+5 with my 3rd and this has never happened before . Anyone know what could cause this? Of course I’m going to talk to my doctor about it but wondering if this has ever happened to anyone else before?