Anyone experienced this?? Advice needed....

LO is 16 months. He's been quite a sleeping champ and he had been STTN since 7+ months (even before that , he'd only wake 1-2 times to breastfeed at night).

However, recently, it almost feel like every other night he'd start waking up once or twice at night. He doesn't usually cry. He'd usually remain quiet and he'd make a loud "ahhhhhh!!" after 10-15 minutes of quiet. Fearing that he could be sick / fever / poopy diaper....etc., I'd check on him after 20 minutes. But when I go over, he'd usually just lay there, and look up at me quietly. After I make sure he doesn't have a poopy diaper or has a fever , I'd go and he would be fine. But again, he'd scream in about 10-15 minutes. This sleepless period lasts about 1-2 hours.

I usually don't change him unless he has a poopy diaper as I am afraid it may wake him more (he is the type that doesn't even mind sleeping in his own poopy diaper). There was 1 night it just lasted for way too long so I changed him anyway. Still doesn't help. He still won't go back to sleep. In these cases I just had to close my door and turn off the baby monitor so at least I can go to sleep because he seem fine.

I suspected it could be ear infection (he does have a history of this and he has a cold now), but I'd think he'd be crying more painfully instead of just looking up quietly at me (sometimes smiling). He also doesn't have a fever. I am hoping it is teething because one of his molars already cut through, and he has a whole mouth of teeth.

I can't help but think maybe he's napping too much, but I don't think so? He naps mostly 2-3 hours in 1 single nap a day. Then we put him to bed at around 7pm.

Have any of you experienced this before? What could it be? I kinda don't want to take him to the doctor because I am afraid they'll tell me it is ear infection and give us more antibiotics.... but he is really fine.