Does this sound like depression?

[cheesefootballsarelife]

Feel tearful all the time, like I've had some really bad news. Totally exhausted but can't sleep. No motivation for anything.
Feel completely useless and out of my depth in several work situations which wouldn't normally phase me.
Irritable with the kids

Yes it does but you do need to visit your GP to exclude any physical issues such as thyroid. Either way GP really is the best place to start xx

Diagnosing depression tends to be carried out by a Dr using a PHQ9 test. You can take the exact same test online (patient.info/doctor/patient-health-questionnaire-phq-9) and that will give you an indication that you MIGHT be suffering from depression. Its not a definitive methodology, but its the one Dr's in the UK tend to use. As has been said, speak to your Dr and get some advice.

Depression can be a passing thing and you can also have things that make it look like you're suffering from depression like not sleeping well. It doesn't mean you're weak or can't cope. You've just realised you need some help at the moment due to life and considering how hard life is for many at the moment, that is understandable.