Period while pregnant,??

Women who claim that they got their period while pregnant, did you get PMS symptoms with it? Was the flow the same? and did it feel like an actual period?? (As far as the pain? cramps, back aches, etc) Because I’m confused. You cant have a full on period while pregnant, that’s impossible bc you’re shedding your uterine lining...So women, please explain. What is the difference between bleeding while pregnant and your period....(A positive test in one)