Hello and hope you are doing well.
Understand your predicament.
Polycystic disease of the kidneys can be autosomal recessive or dominant. The recessive variety manifests in childhood, while the dominant one in adulthood. If the disease has affected the kidneys considerably then it should reflect in the kidney function tests. Also, the cysts are likely to get infected and can lead to symptoms of fatigue, fevers and pain. Please discuss this with your doctor am sure he will provide further assistance.
Hope this helped and do keep us posted.
Pain in the lower back and flank pain as well as headaches are symptoms of polycystic kidney disease (see private message).
Have you been regularly getting your red blood cell count monitored (with kidney disease, there can be an issue with erythropoietin, a hormone instrumental in red blood cell production) ? What about protein in your urine- how much of that do you have in a 24 hour period? What is your glomerular filtration rate (GFR)?
Have you had your iron, iron saturation, and ferritin levels checked with your chronic tiredness and headache to be sure you aren't iron deficient, as these can be symptoms of iron deficiency and the menstruating female often is?
You say you are fighting to keep weight on. Have you had your thyroid function checked, and if so, with what results? Are you eating normally or are you having trouble with eating because of the stress you are feeling?
Your blood pressure is something you need to keep a close eye on with your kidney condition. Do you have high blood pressure or are you trying to control high blood pressure with medication? If the answer is the latter, I believe a number of those blood pressure medications can tend to make a person feel tired.
Since you mentioned yu have been having the problem since having your child, have you gone back to the ob/gyn doctor for a check up to see if there may be something wrong in your reproductive system? Have they checked the lining of your uterus, done any pelvic ultrasounds, and are menses especially painful for you?
I don't think it would hurt to get a second opinion from another nephrologist at this point also regarding your kidneys' condition.