E.W.
My daughter was doing the same thing (20 months), she used to go down wonderfully and now she puts up a fight. I read The Happiest Toddler on the Block and tried one of their methods it has worked great. What you do is start singing a song, then say "Mommy will be right back, I forgot something" (or just any old reason to get away. Then you leave and come back, you repeat this a few times staying gone a little longer each time. Eventually they fall asleep waiting for you. This has worked great for my daughter and now I really only have to leave once or twice, we have only been doing it for about 3 days but I have a feeling she will start going back to bed by herself very soon. Hope this helps