when I walk I feel something weird in my lower leg, about 2-3 inches below

[Lola]

my right knee&an inch to the left? it is a small area but feels sort of tingly and almost like something under my skin is loose and jiggling around. when I am not walking, I dont feel this, but I do notice a slight pulsating sensation. It started about 3 pm yesterday. I have nothing visible on the surface like a bite or rash or anything. I have no other symptoms of anything else like a stroke or blood clot, and it is only in that one small area, about an inch or 2 in diameter. what could this be? I have been taking antibiotic since monday and will finish my dosage today. can that have anything to do with it? Im a 33 year old healthy female. I dont smoke, I dont drink, I dont have high blood pressure or diabetes and I eat a healthy diet. at what point should i go to the E.R? Im a little nervous about it