C.C.
Yes, dont worry, this is an adjustment phase. My son's naps have got shorter and shorter. He is 3.5 and sometimes he skips a nap. But then he will fall asleep no problem before he even gets to bed. It is normal. They are very excited about things we take for granted and they usually dont fall asleep until they are ready to drop. Avoid too much TV also. This disrupts their sleep patterns.
What you can try when he looks ready to take a nap is to lie down on a playmat with him next to you and read him a story, or make up one and watch him start to close his eyes. It has even put ME to sleep. LOL