If you have worn heels for a long period of time, it can take a good while to get used to wearing flat shoes. Flat shoes can cause some foot types to be positioned in a way which can cause issues such as big toe joint problems, heel pain, knee pain, callus or in some cases, a combination of issues.
If you have a low arch profile and a flexible foot, flat shoes may be the worst type of shoe for you. A shoe with a maximum of a 2-inch heel is usually the best for this foot type.
Modern flat shoes usually focus on fashion rather than support and fastening. This means that in some cases the foot holds on to the shoe rather than the shoe holding on to the foot. This causes toes to flex and the tops of the toes can develop pressure points which is perfect for a corn to form.
Foot pain is not normal and usually to decrease your foot pain you should start with your footwear. You should identify a shoe that eases the pain and consider visiting a podiatrist as they can advise on the best footwear for your foot type.