I wrote this in a chat and then realized that maybe sharing my experience with everyone, might help someone. So here's my story.
I too, have CKD 3A and I also was given the, "ok you have it, see you next time!", from my GP and even from the first nephrologist I went to. It didn't seem right to me so I took it upon myself to get the ball rolling. I don't have diabeties so I cannot speak to that or any complications between the two. The sooner you act, the sooner you can hope to get your CKD stable. My has been stable for 3 years, maybe longer.
#1: I found another nephrologist, then asked my GP to write me a referral. This nephrologist is a saint. He took the time to answer all of my questions. I told him about 4 other doctors who brushed it off and that I thought, the earlier you treat it, the better. He agreed with me.
#2: I found a nutritionist at the same clinic/within a hospital. Then I did the same thing and got a referral.
#3: Diet. Even though my nephrologist saint said that my body can still handle any potasium that I give it, I still track it daily. Along with sodium, potassium is usually the second highest level ingredient in many foods, and is bad for your kidneys if you eat too much of it. I also watch my sodium daily. That's another one that knocked off a lot of foods I ate. Phosporus is another to keep an eye on, but I have not found it to be a real issue in the foods I eat. Avoid processed food. That finished off all of the foods I was eating. My eating habits are terrible and I always grabbed whatever was the easiet. The dietician has me taking Vitamin B12 with folic acid. The folic acid should be around .8, which is what I think most vitamins have. Watch for sales. Vitamins are always on sale. Look up some food lists because there are foods on the list that you might not consider ones to avoid. Look up Fletcher Allen Healthcare-renal nutrition services, and kidneyfund.org. They have some great food lists and lots of information. There are also a couple of groups on FaceBook that share info and recipes.
#4: Exercise is important for kidney health, actually overall health anyways, but like your heart, it is especially good for your kidneys.
#5: My GP has me going in for lab tests every 6 months. They may not check for vitamin D, but again I just asked them to include it, and be sure to fast each time whether the doctor tells you to or not. Just tell the phlebotmist that you are fasting and they usually note it on the report. If not, just tell your doctor that you fasted ahead of getting your blood drawn. Fasting will give the best idea of where your levels are because they are not being influenced by food. I always make my appointments early AM so that there hasn't been any food in my system for 9-12 hours.
I was really concerned (afraid!) of what CKD was going to do to my health, but I took charge after some research and concern for my health. I cannot believe that many doctors look at stage 3 and say, 'meh.' Research, consult, question and question again, and talk to your doctors about what you'd like to do and ask what they think about it. Do what you think is best, within reason. You are your own, and maybe only, advocate.
This is only my experience with CKD. When I was told I had CKD, I was at stage 3 and stayed there for a long time. Some years ago, maybe 3 or 4, my numbers went up and I was/am stage 3A. My numbers have been steady since, in fact once I got consisitent about looking at food levels, some of my blood results levels changed to be more positive. Some are minus when they are a positive thing and some are negative as a good thing.