and, one another thing , little bit off topic, but man's manhood is directly connected to his overall health. It's the proven scientific fact. If for some reason man is not having a harder erection or normal morning wood, it is the onset of various diseases like ailing heart condition, poor kidney function, clogged arteries, blood pressure, diabetes, stomach cancer etc. I've been into this penile health obsession since 4-5 years and it has brought nothing but overall good health. Every day morning wood, higher energy level and no fatigue day. I gulp various supplements like L-arginine, L-citruline, red korean ginseng, aswhagandha, turmeric pills every single day. I've been able to maintain 21.59 cm manhood with the help of extra tool like bathmath and tantric yoga, of course 3-4 days a week workout. Having a good hard erection means you are in good shape, and this applies to man only.

You must be recklessly careless about your health in the past. Seems like stress must have played big role too. Off all the supplements that I take, especially L-arginine is extremely good for your case and it shall help with your GFR. I would still drink that soury cranberry juice before bed, and occasionally plain cilantro smoothie. I mix it with my other smoothie but in your case, I don't think your kidney can tolerate anything high sodium or potassium so just start cilantro smoothie, lemon for taste.

here is L-arginine journal
http://www.ncbi.nlm.nih.gov/pubmed/15252778

Buy it at amazon, go for the well reviewed one. Take care and don't worry much. But at least share, what prompted you to get that test.