Sharp burning pain left side mid back and down my side for 3 weeks, no injury, 2 years ago had a 1.7cm left kidney cyst, could that have grown?

Possible but need to: also take into account your past history of swollen glands, thyroid nodules, and left kidney cyst that should be followed up and measured by US. Have an integrative physician work with you to balance these health issues out. Have your iodine levels checked too, especially if you have a tendency to form cysts, fibroids, fibrocystic breasts. Burning pain is not normal and can be an irritated nerve.

May be cyst rupture: Solitary renal cyst do not grow within the time frame described but may have been growing and finally ruptured. The nature of the pain "sharp and burning", somewhat atypical but well its location and radiation sound typical for symptoms from a solitary renal cyst. Usually, such renal cyst pain also accompanied by gross hematuria in case of cyst rupture which can happen. Renal sono and UA helpful.