K.Z.
We went through this too at around 18-19 mos. I think it was a growth and development stage. My son wanted to nurse all the time, day and night, like a newborn for about a month. It was driving me CRAZY! I tried to deny him, but he would just throw fits. I tried all sorts of things, I was at wits end!
Once I realized he "needed" to nurse, for whatever reason, his little body just needed that, it got better! No kidding! Once I relaxed about it and calmed down and stopped worrying that he would NEVER stop nursing and just decided in my mind to enjoy the time we had together, it was easier for me to deal with. And that made all the difference for him too.
I went back to welcoming him in my arms when he asked for "Boobie Time," and stroking his hair and singing to him like I always had when he nursed. He began nursing less frequently and for shorter durations. I think he just wanted to know it was there when he needed it (as it always had been, only I had begun to pull back), and when it wasn't a struggle, he was OK again.
Around 22 mos my son began sleeping through the night on his own, without any "working on it" from me. He slept 8-9 hrs and hadn't done that but a couple of times since birth! He just stopped the middle of the night nursings and started sleeping until morning!
I know every story is different, but maybe the part about relaxing yourself and not fighting it will help! Good luck!