Why does the bottom of my heel hurts when i step on it?

Plantar fasciitis : The most likely diagnosis is planter fasciitis. This is inflammation of your large ligament that inserts into your heel bone. You should get this evaluated by podiatrist. In the meantime you can do calf stretching, massage the ligament with a frozen water bottle or something similar. Anti-inflammatory medication will help as well if you can take it.