Well if your diet is crap it’s not enough to stop eating things - you need to add good stuff.
Find the best veg box delivery in your area, whether that’s a national outfit like Riverford or Abel & Cole, or something more locally based. Buy the largest amount of seasonal fruit and vegetables you can afford, consume and store weekly. The good thing is, the more natural, nutritious fresh food you eat, the less room you’ll have for the other things.
Why were you eating rubbish? Absence of decent food sources nearby, or outside every possible decent grocery delivery? Illness? Or failure to organise and manage food shopping so you’re always ‘grabbing’ something last minute? Do you eat lots of takeaway and processed food? Any or all of this needs addressing.
If you drink - cut out alcohol completely for three months. You’ll be amazed within a month at the difference to your energy levels, skin, and general mood. And you’ll probably find you want to drink less, going forward.
One other thing - do you see a dentist regularly? Perhaps you do, but if not, move heaven and earth to either get onto a hen's teeth NHS list, or pay for private healthcare. Poor dental health can be unbelievably bad for general wellbeing.
However - you would also be wise to get a check up at your GP surgery. There may well be one specific thing that needs tweaking - find out.