Dear Mikaela,
I donated a kidney 16 years ago, to a stranger, and I am doing fine now at age 72 (I even run half-marathons now and then.) Please be aware that depression after kidney donation (even when the donation is a complete success) happens to MANY donors. You are NOT alone. I myself did not suffer this, but over the years I have read of many such experiences. Better transplant hospitals warn donors ahead of time about his danger. They can be many reasons. The operation itself, of course, is traumatic, and the body's hormone levels can be disturbed by the loss of the kidney and also possibly the effects on the blood supply to the adrenal gland above the removed kidney. Also you have the after-effects of anesthesia and pain medications. And there is the "let down" after such a long period of anticipation and preparation. Some doctors compare it to the depression that some mothers suffer after giving birth, even though all went well and they very much wanted to have a baby. So don't be afraid to seek help from a counselor or psychologist or doctor. It is NOT your fault. It appears to be a sickness like other sicknesses. Very painful, but can be helped.
You might want to also post your message at the FaceBook page of Living Donors on Line, as now many more donors post there rather than here. There have been MANY donors there who have shared their experience of after-donation depression.
best wishes and prayers,
Fr. Pat