Feeling Trapped in NFP

I've found a couple of other blogs by Catholic mothers of young children.  Like Conversion Diary, these blogs are written by Moms who practice only NFP to space children or avoid conception altogether.  Most of the posts and comments on the topic of NFP are upbeat.  In one comment, however, a young woman complains bitterly.  She writes that she was raised by parents who practiced NFP and that her mother was a fanatic on the subject.  The young woman herself has stayed the course but fears it's ruining her marriage.  She thinks that her Protestant friends who use artificial contraception have happier marriages.  NFP permits sex at the time of the month when she's least interested in it and prohibits it when she's most interested.  She's ready to quit but can't get up the nerve.