A:

I think I put my back out.
我想我閃到腰了。
I’ve been resting for three days, but it still really hurts.
我已經休息三天了，但還是很痛。

B:

If you’ve already iced it, you can use heat to help soothe the pain. 
如果你已經冰敷過了，可以用熱敷來舒緩疼痛。