Even though i agree with pinkfizz and the gopher ....i do have to say that are you sure that if you find another job with more suitable hours you are not going to feel the same.As a mother myself i had to make a decition about work or not to work ...i decided to work but not untill i had forgiven myself in advance for spending time away from my children, it is a huge pull and the feelings of guilt can be huge , your son will not miss u as much if the time you spend with him is quality this will also help to eleveate your own feelings of inadequacy ....also if you were such an awful mother you would not be feeling the way you do at the moment...i hope you find a solution soon .
Best of Luck