hi, occasionally i use speed, by injecting. About 4-5 days ago i was injecting into just above the top of my hand and couldn't find the vain so i pulled it out and tried somewhere else. Two days later the side of my arm has become red,swollen and most times very painful. I had a script for cephalexin 500mg and have been taking the recommended dose a day and the redness ans swelling has come down quite a bit, but at times is still quite painful, especially if i don't keep my arm in an upright position. am i using the right antibiotics?