I have bipolar which comes with long and unpredictable phases of depression. Sometimes I won't realise how crappy I'm feeling, until something insignificant goes wrong and suddenly I'm connecting the dots to a million possibilities and past events that have unreasonably upset me as well. These thoughts and nasty self-talk build up over time, making the depression deeper and more intense.
Look up CBT therapy if you're interested in this path. This type of therapy focusses on learning about your thoughts and the impact on your feelings and behavior.
Lack of motivation and lots of crying could be a starting point with your GP. They can set up a reduced fee psychologist referral for you.
I found therapy helpful to understand and recognise my feelings, and in turn building strategies over time to strengthen other areas of my life.