Thank you for all of your responses.
Basicaly, he wakes ups crying or wakes up and start to cry (I can't catch exactly how it happens), but once my husbabnd or I give him pacifier and put him down, he goes back to sleep.
I am not sure if I should put him earlier to bed since he has only one nap now and probably really tired.
BTW, he is teething!!! I just felt his fifth teeth (second right top tooth)... and he was crying longer than usual last night when he woke up. But usually he goes right back to sleep once we get him his paci and put down (since he usually sits down or stand up once wake up).
I'll try to put more pacifiers into the bed tonight (but I am not sure he is even looking for them because when he tries to find it, he usually does and then goes back to sleep).
Thanks again for all your help.