J.F.
My daughter is now almost 5 months, but at 3 months we had the same problem. I agree with the mom in the earlier comment and just go with the flow. It took a few weeks, but now she is taking more regular naps - a small one in the morning (45 min - 1 hr) and a longer one (1-2.5 hrs) in the afternoon. I have realized very quickly that caring for your infant is not an exact science. At this age, even having the exact same routine everyday, does not necessarily give you the same results everyday. Hopefully that will come later. :) We just looked for her sleepy signs and gave her the opportunity to have a quite place that she could fall asleep. If she did, great, if not, fine too. Eventually she will learn to take those opportunities to sleep. Be patient and good luck!