good info BP!!!
i have to say my DS was never a good day sleeper and prob did the 45 min cycles upuntil about 1-2 months ago when they started stretching out to about an hour (he has 2 sleeps a day now).. ij the last month he has stretched them even more, we now get about 1.5 hrs at each sleep (give or take). i hope you find something that works for you sooner than this (my ds is 12 months) but just thought i would add this as it does eventually sort itself out.
my ds was rarely overtired, he just did lots of short sleeps when he was tiny. will he sleep in his rocker if you bounce him? do you have a sling to carry him (he may sleep in there)? both of those worked for me. good luck!