New here - is this anxiety?

Hi all
This is my first post on this site. I come here, desperate to know what's wrong with me, and if what I am experiencing is anxiety or depression or OCD or Obsession.... please help! This post may be a big long - please bear with me. This is the very first time I'm putting something I've struggled with for years, in words.

I have the habit of getting stuck on something sad (sad event, conversation, situation) of someone else (never myself)... and obsessively looping them in my mind for days on end.
I also seem to put myself in the shoes of the person who is going through something sad or tragic and imagining how they must've felt at that time, and attempt to feel the emotional pain. It is of course not always possible, hence the looping till I feel it (the feeling is fleeting and momentary) and then I start all over again.

Eg - I used to volunteer with a foster child. He was showing no interest in homework and I finally lost patience and started nagging him about why he doesn't do his homework (like I nag my son sometimes - "why don't you pay attention to your homework, why don't you do this.. do that.."). In the middle of my sermon, he shouted "BECAUSE I MISS MY MOM!!".
I started crying and held him close and we talked about his mom.

That was 4 years ago.

I've spent all of this week, replaying that moment where he said he missed his mom. I've been putting myself in his position and trying to feel what he felt. How sad he must've been. How much he wanted his mom.

It happened. 4 years ago. I am not in touch with him anymore but most likely, he was adopted by a family he liked (which was in process when I last had contact with him).

Why am I stuck on that sentence of his, replaying it over and over, crying, staying up at night, and most painfully (for me) - putting myself in his shoes and trying to "Feel" what he was feeling. It's driving me crazy. I can't focus at work. I can't sleep. The trauma of my interaction with this little child who was in so much pain has come back in a rush. FYI - I spent two years volunteering with him. Loved him.

This is just one example. This is what happens even when I read terrible news articles about a child or animal suffering. I zone in on the moment of pain or tragedy and try to "Feel" their pain.

What is wrong with me? Anyone else experience this? What can I do? Who can I go to for help? Please help.