I too had the nursing agitation during pregnancy and it began in the beginning of the 3rd trimester and wasn't so bad at first but was horrifying the last month of pregnancy getting worse and worse, there were a few points where I was biting my arm or hand just to try and get some distraction.... ok sounds crazy but I had a tough time getting our nursing relationship back when my milk dried up and dd began biting when she was about 10 months, for two months we were in agony over not being able to bf because everytime she'd latch she'd chomp down and bite not even trying to nurse. It was frustrating for both of us and I kept trying and 2 months later she stopped biting and began nursing again. I LOVED the bond and nursing relationship with ds and that lasted til he was two and I wanted it for dd as well, so I have been determined to tough it out...
And I am sooo glad I did! I wanted to tandem nurse and read about other mommas who did and wanted to help dd have a relationship with the new baby as well so she wouldn't feel like the baby is taking her place.
So I bf both, when baby nurses dd comes up with a pillow and asks to nurse and it is sooo precious when she does cause she is feeling all over her sister and holding her hand... oh I just love that. If she starts wriggling around though I tell her all done and she's usually ok with it and will go find something else to do, she just wanted to make sure that she still has momma's attention. She will come up at other times and ask to nurse at first I made sure to give it to her everytime she asked since I think it's just her asking for reassurance, after a few days I started telling her no after a few times and sometimes she's ok with no and others she still wants it. I try to get her interested in something else for about 10 minutes but if she is still asking I go ahead and let her nurse.
She also nurses to sleep so I usually have both girls nursing off to sleep in bed at night, once she's out she's out, so far no midnight nursing for her just baby.
Perhaps you could try what I've been doing and you don't always have to let them nurse till they are done, they rarely will just pop off and do something else, Seraphim will pop off to kiss me or look around and thats when I put it away and tell her to go find daddy or her brother.
She seems to be adjusting really well to life with a baby and I'm thinkin it has a lot to do with the way I'm handling things... but I could be wrong and it's more about personality but really this girl is a mommas girl and "high needs" in all honesty.
Hope things get better for you! I still deal with some agitation but it's usually at night and I seem especially prone to it when I have on a larger pad or need to change it, sorry if it's tmi but I've found that a smaller pad and constant changes keep me more sane, I'm normally a tampon gal.