The medical term for emotional numbness is anhedonia.
It's a dysfunction in the dopamine reward system in the brain. Besides lack of emotional response, it often causes unwanted negative thoughts, the "constant battle" you describe. It's found in lots of different brain disorders. It's THE classic sign of depression.
I found it one of the most painful parts of depression. Especially when it's low grade and you're not crushingly depressed, you just don't feel anything! Numb to life, like a zombie.
Anhedonia is what saved me, in a strange way. I'm a Christmas geek.
I love Christmas and everything about Christmas. Goofy shirts, twinkly lights, ho-ho-ho, fake snow, everything. I had been struggling with my bipolar disorder for several years on my own till one year I heard the first Christmas song on the radio and I felt nothing. I was numb through the whole holiday, even kids opening presents - nothing. I was devastated. Needless to say I was in the shrink's office in January and two months, and an emotional 180 later, I was trying to figure out what took me so long.
Get help now, don't wait. You don't have to just endure this!
PS - the medical term for low grade depression is Dysthymia.