I Believe I Have An Abscess. It's Been A Week

I believe I have an abscess. It's been a week and a half and it's not getting better. I was given amoxicillin which didn't do anything. Went to Urgent Care and they did a sonogram but found no puss and switched me to two other antibiotics. Since then, the spot remains painful and has changed to a dark red/purpleish color. Compresses aren't helping either. Help!