bad mother

i have a 6 yrs old son i love him n i hade i bad relationship w the dad now everything is better am pregant n w my new partner baby he excited n ready to do all this things w the new baby but am not i feel guilty as a mother cuz i cant feel that emotion of having a new baby its like why does this child enjoy n gets everything but i suffer w my 1st or is this all in my head n i got just relax ????