M.P.
Hello! I don't typically disagree with other responses, but thought I should say something in regards to Jenifer H. I don't believe children this young should be going without a daytime nap at all. Even adults need a daytime nap from time to time! Children do need their sleep, and from the sound of it you do know your child and he does need to take some sort of nap in the daytime. Kids this young will get overtired without a daytime nap and this can affect nightime sleeping.
My son is 21 months and he is doing the same thing as your son! At each new stage/phase they hit their sleep patterns change. It could be he's out of a growth spurt or as he's getting older he just simply needs less sleep. As this adjustment happens he might seem cranky and not "quite settled in" to the new schedule, but he should get there over the next couple weeks. Think back to when you were younger and school just started in the fall, remember the "adjustment" your body had to make on getting up to catch the bus? Maybe 2 hours for a daytime nap will work out for him, but right now it's kinda rough to adjust. I wish you the best of luck, and keep us updated if you can - you are not alone! Just remember, sleep beckons sleep, this statement has held true for us and helped, especially for a non- sleeper and colicky infant like we had in the early months. Blessings.