i did resort to sleep training as i was in the same boat.! And when i say what we did you are never going to believe i was in the same boat and she WOULDN'T be put down and loved being rocked.
i bought the alison scott wright book( saw it and never heard of it, but thought it may help me), as was really at my wits end with rocking or having to go out in car to get her to sleep. haven't really read any other bits of the book, just the sleep training bit and it certainly did the trick.dd was terrible at sleeping in the day and i was worn out with rocking and taking her out. you are knackered enough!!
basically coming up to 2 hours, i take my dd to her room, change her, half swaddle her so arms are out ( could do sleeping bag thing but i decided to make a difference between night and day sleeps to her), give her a cuddle, put her in the cot, stroke her head and pat her tummy. all the time 'shushing her' and saying' sleepy time'. she responded so quick couldn't believe it! obviously at the beginning of starting this, they don't settle straight away so after a few minutes i would go in and do some shush's and sleepy time, stroke her head and firmly but kindly say 'sleepy time' when she looked at me with bottom lip quivering! i kept repeating until she got the message. i think the key is to get them when they are not over tired, cause this would never work, as they are too' animated' and get too worked up. also to not linger when putting down and to assess with a bit of crying dying down, or building up, when to go in.
she had found her fingers at a similar time, so maybe i got lucky with self soothing. some days its better than others but she now knows the routine and craves it almost ( ok now she won't settle when we are out! - but its a better problem than before!!)
try the book. it really was a god send to me on the sleep bit