Please tell me the secret of how to take care of a 5.5 month old while 5 weeks pregnant with another…

Please tell me the secret of how to take care of a 5.5 month old while 5 weeks pregnant with another all while having awful cramping and nausea. I feel so bad because I am exhausted and physically feel sick and am doing my best to be a good mommy to my son. My SO takes care of the baby during the day while I'm at work so when I come home it's my turn which is fine but I literally have zero energy. Of course I'm feeding him and changing him but not playing with him as much at the moment because I feel physically ill. I feel like a crappy mommy.