For me, the ONLY thing that got me out of the 45 min nap rut was adjusting the atimes so that she was tired enough for a longer nap. She was also about 5-6 months when we finally got it situated (it started at 4 months and I did a lot of failed attempts at extending in other ways before I figured out my atimes were way off and then it takes a while to make the adjustments). I know your LO is a lot younger than that, so maybe the cause is something different, but maybe adjusting atimes would work for you too... What I would suggest is lengthen out the first atime in the morning by 15 minutes for 3 days. If you get a longer nap, great, if not, increase atime again by 15 minutes for 3 days. Keep extending every 3 days until the nap gets longer.
One thing to watch out for though - if the nap suddenly drops to 30 minutes, you have gone too far OR too fast in extending atimes, so you'll need to scale back down again for a few days. The atime guidelines on the FAQs around here are just that - guidelines. A friend of mine has a baby that is 6 months old and has a schedule like an 10 month old, but it works very well for them. But some people have older babies with much lower atimes than normal so it all depends on your own LO.
So if your first atime is 1.5 (for example) and you extend it first to 145 and then 2 hours and you get a longer nap, stop there until the nap shrinks back down to 45 min for 3 days (at which time you'll know you need to extend again). Once you get this longer nap, you can start extending your second atime as well. Keep in mind that 45 min naps a lot of times mean undertired (UT) but 30 minute naps mean OT. You don't want to get OT - and it can build up over a few days, so what works at first might still cause OT. This is why it's VERY important to do all this very gradually. I'm also assuming you have your feeds worked out to a pretty consistent schedule...
HTH. Good luck.
