Could you tell me why my heel feels like it is splitting but it isn't?

Plantar fasciitis: This could be plantar fasciitis, which is a fairly common condition in which the fascia (the "gristle") at the bottom of the foot gets inflammed, causing significant heel pain which is typically worst in the mornings and worst with walking. Stretches, anti-inflammatories, and gel heel cups are a good way to start with treatment. http://orthoinfo.aaos.org/topic.cfm?topic=a00149.