*Raises hand and waves it all around* Major catnapper here. She sleeps like a dream at night. She used to nap wonderfully, 2-3 hours at a time...then one day a couple weeks ago she just started waking at 20-45 minutes. She will only sleep one sleep cycle! Occasionally she will self settle once and hit 1.5 hours, but I can't replicate it for anything!
We swaddle, we nap in the swing, we use the vibration, we use white noise. We have tried a million combinations and variations of the above. We have tried the stroller, the baby carrier, we have tried unswaddled, one arm out....
I am currently timing and waking UP my 2.5 year old and trying to keep my 3 month old asleep.
Also, she will sleep in the car (sometimes, unless she is screaming her heart out) but wakes as soon as you stop moving. You can even keep the engine running and she will wake up (so drive thrus can cause her to go from happily sleeping to screaming the rest of the way home).