First paragraph:
I started tracking myself after being warned by my primary care doctor about the fact that my sugar level and blood pressure is too high and that I need to lose weight
This is good. You could change "need" to "needed" (past tense) to make it fit the story about the doctor, but informally it makes sense with "need" because it is a fact about your present condition.
He recommend that I should exercise or at least walk, which I am at least certain of.
The word "recommend" needs to be changed to either past or present for this context. Either "recommends" or "recommended". I would suggest "recommended" because you are telling a story and that would referring to him in the act of giving you a recommendation. "Recommends" would work too because that would be you directly telling us a fact about the doctor which is still true.
He also probably tell me to eat less, of which I am less certain of.
This is incoherent to read because you were telling us a story about your doctor, and now it seems like you are guessing what he would tell you in a hypothetical situation. "Tell" is a future tense verb so it sounds like a hypothetical future where you ask your doctor and see what he says. On the other hand if you just can't remember, I would phrase it like "He also probably told me to eat less, although I can't quite remember."
Those advice are naturally unhelpful.
This is awkward to read because "advice" is not plural. Also I would leave out "naturally" unless you are pointing to something that should be obvious. Perhaps: "Those pieces of advice are unhelpful."
It's not enough actionable advice.
"Not enough" usually means quantity not quality whereas you seem to be talking about quality. Maybe "The advice is not actionable enough."
Many people lose weight only to gain them back once temptation takes over.
"Weight" is a substance not a plural noun, so "gain them back" doesn't fit. Replace "them" with "it" and it will read smoothly.
Second paragraph:
The only thing that's more substantial in my mind was the idea of self quantification, which is the art and science of conducting scientific experiments and data logging on one self, for the purpose of self improvement.
"The only thing that's more substantial in my mind" reads like an exageration. I would phrase it as "A much more substantial prospect in my mind". ("Thing" is too vague. "Prospect" indicates you are hoping for something out of it.) I would also probably choose present tense "i...
I am not the best writer on the block, but I been working on a self quantification essay. It is of interest to lesswrongers since it is about It's about applying epistemic and instrumental rationality to self improvement in the form of running scientific experiments and data analysis on one self.
If you have any criticism or comment, let me know. Also, it needs grammar fixing since I suck at grammar. Thanks.
Be advised that the essay is undergoing continuous revisions. Some of the content may change drastically.