Sometimes you have to face it, it just isn't going to happen. You cannot write. It's a physically impossibility. If you are ill or have suffered a major life stress you will not be able to write and you should not force yourself. Writing is a draining if exhilarating experience - think of it as a mental sport and yourself as an intellectual athlete. It follows, then, that big life stuff will get in the way.
But then again writing is a wonderful way to deal with the trauma that life throws at us. Just don't expect to be able to do it. If you are moved to write because of your circumstances then write, because it will help. But there is no obligation.
If you are finding it hard to find time and energy to write, the important thing to do is not to blame yourself for failing. Just comfort yourself with the thought that you will return to it in time, when the circumstances are better, when you feel healthier and more relaxed. And remember, there is a lot that can be done by not even picking up a notebook, by merely living observantly and being open to possibilities. You can note down any ideas you have and work on them in your head until the time is right.