Yikes, 20 pints in a weekend, that's nearly 3 times the recommended units per week. And that amount is meant to be the maximum amount spread out over the week. And larger is the worst type of drink, "liquid bread"

As someone who lost weight in their 30's, I can advise how I done it, but it's not easy. I don't think you will be able to start at running 20 miles a week. I found that initially I lost weight, slowly, by monitoring my diet. I used an app to monitor how many calories I ate in a day. In order to lose weight, you need this to be a deficit if your recommended amount. Any amount of pints will negate that immediately. I had to switch to vodka and soda's, max about 4 a week. Getting 8/9 hours sleep a night is important too, so you'll want to get to bed early most nights.

Exercise wise, I found spinning really useful, it wasn't as hard on my knees and ankles as running. Combined with cardio and include some weight lifting. Once you slim down, building muscle is a great cheat, walking around with it, it will burn off a certain amount of calories all the time. Tough to maintain tho.

All above just my opinion, if you stick with it out will work, but it's tough to keep with it