I have never heard of pain in lymph nodes being a symptom, but like oldcoot, I am not an expert here.
There is a procedure that can be done to examine the lymph nodes before full blown surgery to remove the prostate....or before other treatment options are followed.
Here is a cut and paste on this topic from the U. of PA medical center site:
"Laparoscopic lymph node dissection
If there is a good chance the prostate cancer has already spread to the lymph nodes, then it makes sense to check those lymph nodes before having major surgery. A laparoscopic lymph node dissection is a minimally invasive procedure to remove lymph nodes. The surgeon makes a number of tiny incisions just below the navel and, to increase the workspace, pumps air into the abdomen. A laparoscope, a slim tube with a tiny camera on the end, is inserted into one incision and, while watching the procedure on a TV monitor, the surgeon inserts instruments through the other incisions and removes the lymph nodes."
If lymph nodes are involved, the sooner you know the better, in my opinion.