If you get the pain when you put weight on it...notably when first standing up after sitting, it could well be plantar fasciitis... inflammation of the tendon/ligament band under the foot. Not linked to diabetes. Do see your GP about it, and don't suffer in silence as untreated this can be very persistent. There are exercises that may help and some people find wearing a gel heel insert to be beneficial. In extreme cases injections can bring relief. I've had this....lasted several months for me, and very painful at times.