Head banging againts soft surfaces at 1.5yr old?

[vgahdmi123]

I noticed he is doing this for the past few days with more and more intensity.

He is not doing it against hard surfaces but only against soft surfaces, either:

-against pillow
-he will come hug me and hit against my belly
-if i am keeping him in arm to make him fall asleep he can do it against my chest

• it lasts 3-4 seconds but 10,20 times per day

Also he is not doing it with forehead but with mouth that are open at that moment.

First I thought he might be bored and seeking attention but since frequency has increased I want to check is it normal? Also to mention, his teeth number 4 is growing out these days.

One of mine did this often against hard surfaces when they was angry. I mentioned it at a gp appointment and they wasn't concerned. They outgrew it