“虽然我们只有四节课,但是我们还是很忙”用英语怎么说

Though we only have four classes,we are still quite busy.
用虽然.但是或所以,
写了虽然,不能写但是或所以
We only have four classes,but we are so busy
可以不?
必须写虽然吗?光写但是可不可以/
可以,虽然和但是只能写一个