Bel - That's good that Coby's finally getting over his cold!
I had a look at your site - Coby looks like a really happy little one.
Re: the head - don't know that much except that it may just be individual difference. My sisters bub was overdue and has a head circ. off the charts small. Whereas Kyla (at the opposite end of the scale born early) was always ave. in the head and about 15% for weight and height. Her head at the last check jumped to 95%!! Perhaps it just depends on where they are with their growth sputs etc and genetics.
Your boy looks very happy and intelligent - so I wouldn't worry!