Why does it feel like I'm stepping on thorns in the middle bottom foot? It's on the bottom where the arch is

Plantar fascitis. Pain on startup that eases somewhat then gets worse as the day progresses. Perform daily achilles stretches with at least 30 second hold. Wear shoes with adequate support and some cushion in heel or buy off the shelf inserts. Roll the bottom of your foot with a soup can or similar object twice a day for a minute or two. See an ortho surgeon if there is no improvement after a few weeks.