I think there are only two viable options in this case:
1) Do an Access to Medicine course and sacrifice attending Leicester
2) Complete the relevant A-levels and apply for Medicine for 2019/2020 entry.
The latter is the best course in my opinion: Medicine doesn't only demand specific grades, you also have to undergo work experience in healthcare environments to showcase your commitment as well as show involvement in other areas (such as volunteering) to highlight how 'well-rounded' you are. Giving yourself 2 years will allow you to meet the traditional entry requirements and obtain a good amount of experience to ensure a competitive application. Also remember, that Leicester requires applicants to complete the UKCAT, and this time frame will give you time to prepare for it.
I studied Medicine myself for a while until I dropped out, and the application process was incredibly competitive and stressful, to say the least! It requires an incredible amount of commitment, and I think giving yourself 2 years to obtain the grades you need and to showcase your commitment to this career change through work experience and volunteering, will help you significantly.