Dd12 never slept as an infant -- or at least it felt that way. I was an overachiever of a baby book recorder when she was little (she was the first and I was in grad school -- no idea how I did that looking back!). In any case, I don't think that I'm exaggerating to say that she slept in 30 minute intervals day and night until 18 months old assuming that I wasn't lying in the baby book either

!
She seriously never slept for more than 1/2 hr straight other than twice for the first year and a half of her life. I recall waking up one of those times after having slept for a few hrs myself terrified that she was dead b/c I had slept for so long. She stopped napping entirely at around 16-18 months and did finally start sleeping through the night a bit after two.
I tried everything including all of the baby book suggestions that were thrown at me. I was opposed to the idea of crying it out but I did try it once for about two days when she was around one b/c I was so tired. Did I mention that I was also a single mom at the time?
She screamed from the time I put her in the crib until the sun came up. The next night was the same. I took her to Target after night two and leaned in to kiss her in her car seat in the shopping cart and she turned her face away from me -- nearly killed me. That was the end of our attempts at getting her to self sooth. I co-slept, carried her around everywhere, nursed until I was 5 months pg with her younger sister... She just had high attachment needs and a great deal of difficulty with tuning out the world and getting to sleep.
If it's any consolation, she's a fantastic nearly teenager now.