What is going on???

Why is my 6 month old baby suddenly screaming and crying when I lay her down for bed/naps? She’s been a great sleeper. She started putting herself to sleep around 5 months, we didn’t need to sleep train. She figured out how to self soothe on her own. She would fuss a little then fall asleep. But now it’s like full blown crying every single time. Even at night, when she wakes up to eat, she used to lay down and fall right back asleep. Now it’s a few minutes of crying or whining, then asleep. Naps are the same. Nothing has changed. So I have no clue why the sudden change?