Not a medical student, but I currently have offers to study medicine at Edinburgh and Cardiff next year. (Still waiting for Plymouth and Bristol)
It's very important that you do your research. Go onto a bunch of Universities sites and look exactly what metrics they use to measure an application. You want to be looking for universities that don't look at your GCSEs whatsoever and you should be absolutely fine. For example, Cardiff use GCSEs heavily so don't apply there or you won't get an interview.
It can also be really useful to go to a bunch of university open days, often they will have a station dedicated purely to the application and academics and you can talk to someone in their admissions office about your situation. For example, I visited Bristol, Plymouth, Edinburgh, Cardiff, Southampton, Nottingham, Keele and Birmingham before applying.
There are two other very important metrics when it comes to academics: Your predicted A levels and your UCAT
Obviously you want to be trying to aim for A*A*A* but you would probably be safe with AAA. Again look how universities score them, if it is just a cut off then AAA is fine. If it is a scoring system then you probably need slightly higher.
Your UCAT is probably one of the most important things in you application. Some universities won't even look at your GCSEs and give offers purely on your UCAT and/or A level predicted. For example, Bristol give interviews purely on their UCAT cut off (3010 this year). So try and do as best you can on that. I took mine right before the start of Y13 in September and got a 3220 (basically meant I was guaranteed an interview). I used Medify which I found was a really good website but there are plenty of others out there. Again lots of information on how to revise for UCAT online and at open days.
Academics are important for receiving an interview. Apply to universities that most suite your academics (depends on how heavily they weight A levels, GCSEs and UCAT) as you will be most likely to receive an interview. Once you have secured an interview, then it is a level playing field. Most universities will ignore all your previous academics and go solely on how you perform at interview. Get lots of practise with any doctors, healthcare professionals and teachers that are willing to help you.
Definitely something you want to be doing is work experience. Any experience/volunteering you can get in a hospital, care home or even just working (eg bar, restaurant) is amazing! You can talk about it during your personal statement and during your interview. Remember to note down things that really stand out to you. This could be how the Multidisciplinary team works together, demonstration of empathy/compassion by nurses and doctors , conversations you have had with doctors about how the NHS works and any other soft skills you've witnessed/ you've demonstrated. Stuff like this shows the interviewer that you have a good understanding of how the NHS works and makes you a strong candidate.
Try and get onto a university pathways programme close to where you live. For instance, I did Peninsula Pathways (Plymouth uni) and I got a week of work experience, a tutor and online workshops. More stuff you can talk about at interview. If you are eligible and deemed as widening access you might even get a reduced grade offer/ reduced UCAT/ guaranteed interview!
Lets say worst case scenario, your academics don't quite go the way you planned and maybe you didn't have the best UCAT score and you don't get an offer, its still ok!! Take a gap year and reapply the next year. You will be applying with your actual A levels so your GCSEs won't matter (you're actual A levels are proof that you are academically capable) and you can redo your UCAT (you aren't stuck with what you get the first time). Plus you have time during the break to improve your application so you will have a much better chance of getting an offer the second time round.
I hope this helps, don't loose hope! Just by posting this on the student room you have demonstrated how eager you are to study medicine so let nothing stop you!