They sometimes do this when they are overstimulated and or tired
Mine did this starting at 2 months when going to sleep, started doing it now during the day when tired (almost 7 months)
New milestone! Try and play with them more by swinging them in a blanket with your partner or flipping them upside down 🙃
i was reading this could be due to teething, my 8 month old just started doing this within the last week along with other teething symptoms:) Drooling, fussy, hard time sleeping, and shaking his head as if he was saying no
If ur concerned maybe video it and show ur doctor
My 17 month old has done since 6 months and it's actually increased the amount he does it. For some it may be a sign of autism- of course with other concerns if highlighted by a paediatrician (this is the case for my son). For other babies it may just be a phase and something new to them. At 7 months I wouldn't over think it until later on after 1 if your little one does it much more and if there were other concerns alongside