How do I write "but if" in Chinese? How can I express that something happens if another condition is true? (Eng: &quot;Subject ... but if ... subject ...&quot;)
Example:

I usually get up at six o'clock, but if I'm really tired, I sleep until eight.
我常起來六點，但是很累到八點睡覺。　（Can I write this?)
A literal translation to "但要是" is fine here.


  I usually get up at six o'clock, but if I'm really tired, I sleep until eight.
  
  我一般六点起床，但要是很累，我会睡到八点。