hi sir/madam
I have gone through your question and understand your concerns.
In my opinion, presently your entering into depressive state. Your crying spells without any reason or for small issues, pain in chest, unable to concentrate, decreased self-esteem are all due to
depression.
The main reason for depression is
stress. Now, in your case, separation from your friends and lonelyness in the office aroused stress levels in you. As you were unable to cope up with stress, you entered into stress related condition like depression.
If I were your treating psychiatist, i would advise pharmacological management with antidepressant like SSRIs along with cognitive behavioural therapy.
I also recommend to start stress relieving techniques like regular physical activity, maintaing good dietary habits, practicing humour, talk with best friends, going for a holiday trip, practicing mindfulness and
relaxation techniques.