I am really glad you wrote.
A few things that you said lead me to Depression. You said your feeling slowly faded away - that's what happend with some forms of depression. And you mentioned that basically, all that is left is pain - and that's exactly what depression is: pain.
Depression is a brain chemical issue that we don't have any control over - it's like having diabetes - there is nothing YOU can do to control it - it needs to be controlled with medication.
See a Psychiatrist (not your regular MD) for an evaluation (they ask you questions about sleep, eating, feelings etc), it lasts about an hour and at the end of that hour they tell you what your options are.
Medications are prescribed based on your specific symptoms... and this is their specialty, so because you are a first time antidepressant medication user, you will do well on the medication!
I hope this information helps, please feel free to write back at any time for follow up questions.