The fact that you're not doing what you're "supposed" to do means there is a conflict that hinders you. In order to get your tasks done you have to dissolve your conflict(s) first.
However, I am afraid this is not straight forward and something no one on the Internet can do for you.
Suggestions like exercise, a healthy diet and meditation are great advice but there is only so much these things can do for you.
I guess your issues are on a subconscious level as it seems that you haven't identified them yourself. It could be anything, really:
Regrets of the past, a lack of social life, low self-esteem, worries about the future that need to be addressed ...
I haven't cracked it myself but it is astonishing how powerful your own body's mechanisms are that keep you from solving your real problems.
Stuff like never feeling you have enough information to get started or even physical pain that makes you believe you have to solve a health problem (that actually isn't really there in the first place) first before you can do anything else.