pregnancy amnesia 

when a woman forgets how miserable it is to be pregnant and willingly agrees to get pregnant for a second (or third +) time. It often occurs in conjunction with or immediately following the contraction of baby fever after her other children have reached toddler age.

Kerrie: Did you hear that Melissa is trying to get pregnant again?

Ashley: Yeah, she must have pregnancy amnesia.

pregnancy amnesia by M in the big D March 12, 2011