Groin pain right side female 51 had pain 4months goes down thigh into knee?

Hernia Pain? A hernia occurs when the tough connective tissue that completely covers our bodies (under the fatty layer) develops a weakness or true hole and the stuff inside bulges out. If you are having pain, it means that the area had some injury. If there is a bulging and it does not reduce easily, then you need to see your doctor. Otherwise, Motrin or advil (ibuprofen) should help reduce the pain.
Any bulge? Groin pain with thigh pain can be a symptom of inguinal or femoral hernia, but definitely sounds to be related to nerve compression. Evaluation by your doctor and possible referral to a general surgeon, neurologist, orthopedic surgeon, or physiatrist would be appropriate.
Likely Hip arthritis. It is very possible that you are having arthritis in your hip joint with typical symptom of deep groin area pain, at times radiating down to the inside of knee area. Often stiff in am and pain can worsen with prolonged standing/walking. Since you have had this for 4 months now, consult doc for eval. In the meantime, motrin/aleve may help the pain. Consult doc. Good luck.