I'm constantly sad,cry at every little thing and lost interest in everything i used to enjoy. there hasn't been any drastic changes in my life so what could be causing this?

Brain hormones?...: There are many signs that may suggest depression, such as: feelings of sadness or hopelessness, angry outbursts or irritability, loss of interest in normal activities, sleep disturbances, tiredness or a lack of energy, either weight gain or weight loss due to appetite changes, anxiety or restlessness, slowed thinking, feeling worthless, etc... Seeing one's primary care doctor is a good start.