First of all try to remove the source of distraction and force yourself to take only one thing at a time. Open a webpage and read it entirely, read a book from start to finish (not necessary in a single day), try to work on your tasks without background music or podcast. Eliminating the distraction usually improve productivity.
Second try meditation. You can think that is a "radical chic" rubbish, but it really works. Start reading "Zen and Japanese Culture" and "Zen Mind, Beginner's Mind" and try to practice meditation, maybe with the help of an expert. You will see an improvement on focus and clear thinking.
Third, take time off your pc. If you understand that most of what you doing in front of the PC is not valuable, just close it and go out, or read a book, practice sport, cook, etc. Learn to recognise when you're waisting time and do something else. Try to make time at the pc more valuable. Use it for coding and research, not much more.
Improvements take time and consistency. We're used to get everything fast, but your cannot buy self-improvement in a course or a book. So start with basic steps and stop complaining.