Since Oxford shortlists for medicine on the basis of GCSEs, no it's not realistic. You should aim for medical schools that don't score GCSEs (e.g. UCL, Imperial) after achieving appropriate grades to apply in the coming application cycle. Do also check that you meet any minimum GCSE requirements e.g. maths or English language, as these are usually "hard" requirements and you would be automatically rejected if you don't meet them.