My baby is 7.5 months. In the last few weeks he has developed a habit of sleeping only if he has a nipple in his mouth. Even if we rock him to sleep, he starts asking for a nipple when laid down(after holding for good 15-30mins). It seems the only way to sooth him is by offering a nipple. This has become extremely problematic and painful for me. He is mostly bottle fed and we ensure he is not hungry before putting him to sleep. What might be the reason for this and how can I help the situation. I don't want to make him dependant on a pacifier.