A mum sending you loads of virtual hugs here ....
Firstly, well done on fantastic A levels, to be really proud of.
If you were mine (and I've 2 about to go through all this), I'd want to know NOW how you're feeling and help you through it. Don't wait until they're due to visit in a few weeks. Talking this through & breaking down exactly what the issues are, will help no end, I'm sure.
I'd definitely set a target of minimum Christmas to review & set mini-targets e.g. I'll take up this new activity starting on x; chase up y society to see when first meeting will be (you could even volunteer to get things moving if they're short on hands). List out the positives of your degree course (including employability) and what's making it painful - can any of the negatives be turned around or even tolerated (remembering that no degree course is 100% perfect, no matter what people tell you!).
Social scene & drinking culture - I feel for you - hearing this more and more as being an issue (and it was bad enough in my dinosaur days of the '80s). Only way through this I think is finding sporting/ musical/ drama/ whatever clubs, where the focus is on 'doing' something. One of my DDs sounds very like you so this is close to my heart. Bottom line is that there will be likeminded people wherever you are, you may just to have work at finding them .
Also, remember that at least some of those getting trolleyed regularly are adjusting to life away from home (whether it be new found freedom, loneliness, peer pressure etc) - those that calm down over the next few weeks/ months could turn out to be great friends, you never know.
Finally, in my ultra-competitive N London area, where everyone 'simply has to' go to uni, it's astonishing how many change courses/ change unis within the first 12 months. Doesn't get talked about much, but it's a reality. Which means that if reapplying elsewhere for a different course is right for you, you're certainly not unusual.
Is there a pastoral team you could talk to on site? They may come up with some options.
As hard as it may feel, try and see this as yet another step along the way. Uni can seem an end in itself and it simply isn't.
You've been so brave acknowledging things aren't right, this will get sorted, I know it. If you were my DD, I'd be a very proud mum
xx