You may be depressed if, for more than two weeks, you've felt sad, down or miserable most of the time, or have lost interest or pleasure in usual activities, and have also experienced several of the signs and symptoms across at least three of the categories below.

It’s important to remember that we all experience some of these symptoms from time to time, and it may not necessarily mean you're depressed. Equally, not everyone who is experiencing depression will have all of these symptoms;

•Behaviour:

-not going out anymore
-not getting things done at work/school
-withdrawing from close family and friends
-relying on alcohol and sedatives
-not doing usual enjoyable activities
-unable to concentrate

•Feelings:

-overwhelmed
-guilty
-irritable
-frustrated
-lacking in confidence
-unhappy
-indecisive
-disappointed
-miserable
-sad

•Thoughts:

-'I’m a failure.'
-'It’s my fault.'
-'Nothing good ever happens to me.'
-'I’m worthless.'
-'Life’s not worth living.'
-'People would be better off without me.'

•Physical:

-tired all the time
-sick and run down
-headaches and muscle pains
-churning gut
-sleep problems
-loss or change of appetite
-significant weight loss or gain

Link:
https://www.beyondblue.org.au/the-facts/depression/signs-and-symptoms