Hi L.,
All babies need sleep at this age and lots of it! I had a colicky baby, and naps were a constant struggle until I finally figured out what I was doing wrong. It is possible that you are putting him down to nap too late? At this age, he should be taking about 3 naps a day- the first occuring about two hours (and no later!) after he wakes up in the morning. Watch for his sleepy signs (slowing down, staring off into space, etc). If you wait until he starts fussing to put him down for a nap, chances are you have waited too late and the nap is going to be a bust as he is already worked up and overtired. Get him on a schedule for nap time every day, and do a little naptime routine that lets him know what is coming next. For us, we turned on a sound machine that queued him that it is now time for sleep. As for the length of time he naps- as long as wakes up in a good mood, then he has gotten enough sleep. If not, the put him down for another nap in no later than two hours after waking up for the last one. Also, I would suggest an earlier bedtime, which might help with daytime napping. Try starting his nighttime routine around 6:30 p.m. I know you will be afraid that he will take up super early, but the opposite is true. Getting him to sleep before he is overtired is the key to good, sound sleep- day or night!
Good luck!