Medicine Counter Assistant. The most usual way of doing it is to get a job and then work for the qualification.
In your situation I would be looking at this combination in order to gain the qualifications for either a Pharmacy degree or the Pharmacy Technician course. You said that you are in Leeds so that's where I started looking.
Access to Higher Education | Leeds City College gives a general introduction to Access courses.
Access – Science and Health - Diploma (Level 3) | Leeds City College Courses the specific course that I would do.
You can see that in the links it states that you can study for GCSEs alongside the main course. By doing that you would be able to pick up the Science GCSE that you are lacking and improve grades in Maths and English to a minimum of grade B if you don't already have them which would give you the entry qualifications to become a pharm tech.
So within a year you would be in a much better position to move on than you are currently. And in the meantime while you wait for next September you could try getting retail experience in a pharmacy even as a retail assistant if not working in the dispensary. As a dispenser in either the community or in a hospital outpatients at least 50% of what you do is identical to what you do in any retail environment. You just deal with different goods.