My Mobile hotspot won't turn on, on Microsoft Lumia 550. Any suggestions?.

[Rachel S3]

It was fine until a few days ago, but won't turn on at all now. I select the 'mobile hotspot ' in the pull down tab, and it immediately switches off. On settings when it is turned on, it turns off straight away too, and says 'we can't setup mobile hotspot.' Can't think of what could of happened?