I am almost 5 months post natal and have a sore area at the top of my head almost where you would find a babies soft spot. What could this be?

Possibilities. Dermatology is pretty visual, so it's hard to know what is going on without seeing it. Tinea capitis (ringworm of the scalp) can present this way, as can an inflamed cyst, or even a localized bacterial infection (abscess or folliculitis). A dermatologist should be able to help sort this out either by close examination, culture, or perhaps skin biopsy.