I Am Having Pain Inside And In Front Of My

I am having pain inside and in front of my left knee and behind the knee going up into the thigh and hip.Difficulty getting a comfortable position and pain is worse after sitting.this gradually came on for past week but much worse the last 3 days.Have been taking Aleve or Tylenol which just takes the edge off but doesn't get rid of pain.Feels like calf may be swollen also.Not sure if this is arthritis which I do have or should I be concerned about blood clot.I am female 76 yrs old fairly good health.Taking estrogen in patch form for past 25 yrs.