Baby won't sleep on her own..

Three months, 14 weeks, nearly 100 days.. of holding her while she goes to sleep. With the exception of the first few days of life, my girl has never been able to self soothe or able to be put down while sleepy & fall asleep alone. 98% of the time, we end up sleeping with her on my chest. She has to be held, or rocked, or walked around.. something, always, in order to sleep, and even then, if she isn't swaddled or stomach sleeping, she will wake up immediately upon putting her down. I'm starting to lose my mind, it's been like this since the day we came home from the hospital! How do I help baby learn to self soothe and sleep better? Have I doomed myself for letting her go on like this for so long??