Suggest Remedy For Sore Throat With Purple Bruise On Neck While On Erythromycin

Hi I have been on a course of Erythromycin - 10 day course currently on day 7. Originally the right side of my neck / throat swelled up. The antibiotics reduced the swelling and after 7 days I was starting to feel better. However at 5pm today my throat felt like it was in cramp / a little swollen - I have eaten a meal however it was a little difficult to swallow the food. My throat is now very sore and I seem to have developed a deep purple and brown bruise on the front of by neck where my adams apple is. Could you suggest what this is please