I suspect that this is true for a number of people and you're being honest with yourself. I find that frequently skimming social media, mostly twitter and IG, makes deeper reading harder. If you do that even 30 min a day, you're untraining reading and training skimming. the rapid cognitive switching involved with skimming a wide range of topics that fly by on a timeline also trains the neural grooves for rapid context switching over attending to something for a while.

Good luck - might take a few months, but with good sleep and restricting phone use, I would imagine you'll see improvements. Med school is also very hard - my wife's a doctor so I see this up close. Don't be too hard on yourself.