for the last couple of days my cats lower lip seems to be slightly bigger than normal....he is fine in himself and he lets me touch it so cant hurt at all , he is ,eating, drinking, playing ....should i be concerned???

I would take him to the vets. He could have been in a fight or have been stung. It also could be his teeth.

Like Maisy Moo says get it checked to make sure. It's probably a sting or a scratch. However you need to make sure its nothing more serious. Not meaning to scare you but tumours in the mouth generally tend to be very fast growing and nasty so you just need to make sure that its not anything horrible like that.