Work my tail off   

拼命工作，非常忙

例句：

I can't handle it now. I work my tail off.

这个事现在我干不了，忙不过来了。

In the middle of something:

正忙着

例句：

Now's not a good time as I'm in the middle of something.

现在真不是个好时间，我正忙着呢。

Be tied up:

忙得不可开交

例句：

I'm tied up in a meeting until 3.

我开会直到3点钟才能脱身。

Have / get one's hands full:

忙得不可开交、应接不暇

例句：

Nowadays, many people have their hands full with study, work, kids, and have no time traveling.

现今很多人忙于学习、工作和带孩子，没有时间去旅游。