I am sorry to tell you this, but your problem is a lack of self-discipline. When you used to be better at studying, did you have someone who held you accountable (like your mother) and who made you do your homework? If you blame it on the subject matter being boring, you let yourself off the hook. Believe me, there will be plenty of days in your life when you have to do things you either don't like or think are boring. This is true even if you have your dream job.
Find a place to study where there are NO distractions. Well, not a closet, but you need to find a place where there is nothing handy that you might find more interesting that the material you are studying. Then, when you settle down for a study session, why don't you try scheduling your breaks. Make the interval between breaks short enough so that you can go from break to break without losing focus. It might only be 10 minutes. The shorter the interval, the shorter your breaks need to be if you are going to get any studying done, but the point is to set the interval so that you will be successful. Then gradually increase the interval as your concentration improves.
Remember not to make excuses for yourself like saying that the material is boring, and good luck.