Sounds like my LO too! I've always joked that he must be a 'low sleep needs' baby as he functioned fine on short 45 minute naps. He's now 5 months and has dropped his fourth nap and takes 2 longer naps and a short cat nap in the evening. Think the turning point was when he figured out to roll in bed and learnt that he could sleep on his tummy.
Also, this may not work for everyone but I will sometimes gently 'wake' him up after he has been asleep for ard 20 minutes. I put my hand on his chest which makes him stir, then leave my hand there for a while until he drops back to sleep. He doesn't fully wake up, but I think it resets his sleep cycle and then gets a longer nap!