Have you been wearing flip flops, or shoes with no support? If you have done alot of walking in non-supportive shoes, it can cause the symptoms you are describing.
Try filling a water or pop bottle with water and freeze it. Roll it under your foot for 20 minutes at a time, two or three times a day. Give your feet a break from flip flops and sandals. Wear a good, supportive tennis shoe until your foot feels better.
Do not use heat. It will feel good at the time, but can trigger your body's inflammatory response, and can cause it to hurt alot worse afterward!