Mine just went through a step change at four months. He was sleeping a lot (but badly, lots and lots of waking) and feeding a lot. He was also a bit whiny and could be quite irritating. He seems to have changed a lot as a result - nearly sitting, rolling over, very chatty, laughing, being much more of a person and much less of a blob.
So I reckon all that strange behaviour was his little brain firing on all cylinders, going through a big change.