How to focus and stop procrastinating?

Im a senior in high school in the rigorous IB at school and from the beginning of time, I have ritually left things to the last minute. I've always finished just in the knick of time, but now that I have a gigantic workload, and I actually find myself not finishing. My remedy for this is usually skipping school to finish, but I've skipped so much school, that I'm at the point where I need a legit excuse to do so now. Procrastinating not only happens with school work, but also in pretty much every aspect of my life such as cleaning my room (unless the cleaning lady does it), I'm always late for school (most of the time by only 2-5 minutes), and in social events (I'm always late when meeting up with friends lol). This has to stop, but I honestly don't know what to do because the stress is starting to cause physiological problems in my body like stomach problems and headaches. My mind is constantly wandering and I think I might have ADD-inattentive. What can I do to stop procrastinating and lower the anxiety in my life because I am literally breaking down :(