How to tell when a baby is teething???

💓 • Momma w a 13 month old 💙

My baby normally sleeps through the night, he hasn't waked up once through the night in months, just recently he has started waking up every 1-2 hours crying, I can't tell if he's in pain or not. I can't sit him down at all or he will cry, and even when I'm holding him he squirms and acts like he doesn't like it. He will barely nap. So far today he's taken one 10 minute nap and he looks exhausted he's been crying literally all day and I just feel so bad I dont know what to do 😫 he isn't running a fever I gave him Tylenol just in case but it doesn't seem to be working. Is there any way you can see if he's teething or not? I looked in his mouth and it just looks the same as it always does, I really don't know what's wrong

He'll be 4 months on the 16th