Ds2 has always had short phases of doing this - repeatedly pushes his lower body against chair arms, bed edges etc. But atm he is doing it for long periods of time - up to an hour at nght sometimes. He gets very cross if I try to divert him.
The obvious cause is self stimulation - he often gets an erection while doing it - but I remember reading somewhere that this sort of behaviour can also have a digestive cause.
Anyone elses child do this and can you pinpoint a cause other than the obvious!