Please speak with a doctor
about this question. A podiatrist
may be the best place to start, as this is a health care provider who deals specifically treats problems related to the most distal aspects of the lower extremity. Your primary care provider may also be able to provide valuable information and some of the simple ideas for what could be causing your problem. Often, it is appropriate for a primary care doctor
to provide a first attempt at treatment before speaking with a specialist, but this can be altered depending on the level of acuity of the problem and the concerns that you may have.
There are several things that this spot could be. First, it certainly could be a wart. The viruses that cause these are very common, and there are some over the counter medications that can be quite effective at treating these. As you have suggested, if it is not getting better with this kind of treatment, it is effective to speak with a doctor. Just like any other body part, you can get moles and other skin lesions on your foot. In some rare cases, these can be signs of skin cancer. Another possibility is a sign of infection. Please speak with your doctor.