Why won't he eat??

First time mom here. My son will be 15 months on the 18th of the month. For the last few weeks he has been the pickiest eater in the world! He normally eats absolutely everything and is hard to keep full. But lately he picks at his favorites or refuses food completely. He doesn't seem to be losing any weight and is drinking enough milk. He was sick with a cold before this started, but seems fine now. He is also always teething these days. 🙄 Is this a leap thing? A teething thing? Should I be worried? He sees the doctor next week for his checkup and I plan to mention it. I'm just wondering if anyone else is experiencing something similar with this age. Thank you!