M.R.
Fortunately my 21 month old son sleeps fantastically, but it was rather challenging from birth to 6 months.
I read Dr. Marc Weissbluth's "Healthy Sleep Habits, Happy Child", instituted the techniques to the letter, and my child was sleeping wonderfully within three (yes, that's right...three) days with very little crying. Dr. Weissbluth is a practicing Chicago-area pediatrician with over three decades of infant/child sleep issues - in other words, he has studied and helped tens of thousands of babies and children with great success.
Only you can choose the technique that is appropriate for your family. Give this book a fair shot and you might just find the answers you and your child need.