It is inflammation of the fashia on the bottom of your foot.
You need to see either a podiatrist or an orthopedic specialist that specializes in feet to get the proper treatment.
Depending on the severity of your pain, you may find that simple treatments will work to relieve your pain and a round of physical therapy will be best for you.
By going to physical therapy, which you need a doctor's order for, you will get some message, ultrasound to the area in pain and learn the proper exercises to strengthen the area of your foot and heal that is inflamed, how to do them correctly and how to properly stretch your hamstrings as well.
It may be that you will need some custom made orthotics as well and you will need to get some good support shoes to wear as well.
One thing to do for now is to never go barefoot. that puts extreme pressure on the bottom of your foot and may be how you developed this.
Also some of the worst shoes you can wear are the flip flops. Both podiatrist and ortho offices are full of teens and early 20 women with this problem and their shoes are the flip flops that have caused the problem
Just google plantar fasciitis and you will get plenty of links to check out on the problems.
Fran