Is "being considerate" something that can be learned or trained?

In a sense it feels like you are differentiating yourself from others.
And yes, I've done the same thing myself in the past.
It feels like you haven't bothered getting to know the people around you properly and closed out yourself from everybody else.

Try asking people more questions about themselves, what they like and more importantly why they like it, actually give it a go and try get to know people better, try to understand them and why they act like they do.
Make it a habit to ask people questions all the time what they feel about things and so on.
As you have been created from your genes and surroundings, remember that is the same for everybody else and you should NEVER look down on anyone else for their shortcomings.

Not being able to relate that much to other people's pain is something I'm guilty of myself, but it's not necessarily a bad thing, rather there is no need to feel bad about someone others pain. You should be the one in support.
As long as you understand it is hurting the person you're talking to there's no need to get all sobbed up yourself.
As a matter of fact, I never give in to sad feelings at all nowadays, all because of this one book.

Well, you asked for self-help books and frankly, there are lots of shit self-help books out there that get you nowhere.
However, if there is one book I should mention, it is "The Power of Now" by Eckhart Tolle.
It is a must read that I recommend to everyone, no matter who you are and no matter how your life is at the moment.
READ IT. It changed my life and hopefully it will change yours to.

Good luck.

Jam it back in, in the dark.