Hello,
From your symptoms it can be drug induced bullous eruptions( if you are taking chemotherapy), bullous fungal infections( common in immunocompromised patients like those on chemotherapy), photophyto eruptions or bullous staph infections.
To confirm the diagnosis, please get an evaluation done from a dermatologist.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your dermatologist. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.
Do you have cancer? If so I hope your treatment is going well and encourage you to stay strong! If you do have cancer your feet may be reacting to your treatments. If not, it may be a fungal infection that your body is a having a hard time fighting because of a weakend immune system. You may need an oral anti-fungal to rid of it. Also try putting baby powder in your shoes to keep them dry.