What Causes Problem Of Slow Learning?

Hello, I am a 41 year old female. I have struggled all my life with learning. I was put in with the "slow retarded" kids when i was in 3rd grade for my reading level. I look normal. People think i am smart until they get to know me. I have a problem with spelling, reading, comprehention(sp), math(numbers). The reason it concerns me is because i am divorced have two children and can not get a good job that i can do well unless i settle making $12 dollars an hour. I want to know what is wrong with me. Why can't I learn? Is it possible that i have some sort of brain damage. My mother told me i fell on concret when i was 3. Please help
Sheila