I think he is struggling to get himself off to sleep now that he is bigger and mobile and has got used to you helping him. I?m not sure how you would feel about trying this technique, which I used on my DD about the same age and it did work with a little perseverance over a few nights.
Put your DS into his cot and go through your usual bedtime routine of good night etc and then leave the room
When DS cries pick him up, reassure him by saying something like ?I'm here'
When you have done this put him back down
Leave the room
When he cries return to the room, gently pat or stroke him, avoid saying anything to him
As soon as the crying stops, leave the room.
If he doesn't stop crying pick him up
As soon as the crying stops, put him down
Leave the room
Even if your DS cries as soon as you go to put him down, do it anyway
If he continues to cry pick him up again
As soon as the crying stops, put him down
Repeat this as many times as is necessary until your DS falls asleep
Apart from the first time you go in this should be done in silence.
This approach is seeking to provide your DS with security, to know that it is okay to cry and that you are there for him. It can take about 20 minutes to settle a baby this way, though it can take an hour or more.
HTH :)