I am going through the same thing. Yesterday, I put my LO down for a nap in her crib and realized I forgot about her. I was so engrossed withe the thought of "thank god she is sleeping so I can get some peace" that I wiped her totally about of my mind. I feel the same way. When I am not around her, I find myself not thinking about her and happy that I don't have to be bothered with all the troubles that do along with taking care of her. She too is an excessive spit uper and the formula has ruined nearly every item of my clothing as well as hers. Then she has reflux and is on meds that aren't working. Then there is severe gas on top of all of that. Nothing helps to relieve the gas, spitting up, and reflux and she just screams all day long. On the off chance that I can get to sleep she wakes up 10 minutes later wide awake and crying. God forbid I try to take her anywhere. She screams bloddy murder when I put her in it.
The worst part is someone asked me if I could imaging my life without her and I said yes I can. Talk about feeling like a failure. I can't wait to go back to work yet I dread that her problems are going to cause my mother to tell me she can't take of her and I will be forced in to a situation of figuring out how to afford daycare, which I can not.
Are you dealing with PPD? Are you on meds? Have you thought about talking to your doctor or a professional therapist? I don't think you are a failure, we just need to find ways to cope besides making ourselved feel guilty.