What is the patients diagnosis?

I am doing a lab report for a class and we have a scenerio in which a 40 year old woman is experiencing fatigue and muscle weakness. She says her joints are painful and losing weight. She is also showing signs of depression.

It might be chronic kidney diease.

Having chronic kidney disease means that for some time your kidneys have not been working the way they should. Your kidneys have the important job of filtering your blood. They remove waste products and extra fluid and flush them from your body as urine. When your kidneys do not work right, wastes build up in your blood and make you sick.
Chronic kidney disease is caused by damage to the kidneys.

The most common causes of this damage are:

High blood pressure.
High blood sugar (diabetes).
Other things that can lead to chronic kidney disease include:

Kidney diseases and infections, such as polycystic kidney disease, pyelonephritis, and glomerulonephritis, or a kidney problem you were born with.
A narrowed or blocked renal artery. The renal artery carries blood to the kidneys.
An enlarged prostate gland, kidney stones, or a tumor that keeps urine from flowing out of the kidneys.
Lead poisoning.
Long-term use of medicines that can damage the kidneys. Examples include nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen (Advil) or celecoxib (Celebrex), acetaminophen (Tylenol), and certain antibiotics.

As your kidney function gets worse, you may:

Urinate less than normal.
Have swelling from fluid buildup in your tissues. This is called edema.
Feel very tired or sleepy.
Not feel hungry, or you may lose weight without trying.
Often feel sick to your stomach (nauseated) or vomit.
Have trouble sleeping.
Have headaches or trouble thinking clearly.