When did you start you baby on solids? My DS i...

When did you start you baby on solids? My DS is 12 weeks old tomorrow and my GP has recommended starting him on solids because he has a least 2x 300ml bottles a day plus another 3x 200ml (so 1.2L of formula over 24 hours) and never seems to be settled when awake. I don't see my CHN until Feb (she is on holidays) so I can't ask her advice. Is there anything other than giving him solids that I can do to help him feel fuller? I seem to have hungry babies lol, we started DD on solids just before 4 months of age. Tash