Would a nodular melanoma, or a melanoma of any type grow in 6 months?

It could: Melanoma can do all kinds of things and can be very lethal. Something could be present for years and then sudden;ly change or seem to appear. It should be checked out soon- preferably by a dermatologist or experiened surgeon.

Consult your doctor: If you're concerned about a skin lesion that has grown rapidly or changed suddenly, you should consult a specialist who treats skin disorders. A dermatologist or plastic surgeon could evaluate this lesion and give you advice about how to proceed.