Bedsore - need advice. What should I do?

My mother got a bedsore when she was in the hospital. At that time it was purple in color. She was sent home and I have been taking care of her. The color of the sore went from purple to dark pink. I have been changing the bandage every 5 days. She now has the flu too after leaving the hospital a few weeks later. Now all of the sudden the middle of the sore has white puss the size of a 50 cent piece. It is dark pink around. I think it looks worse as their was not puss and it concave a little where the puss is coming out. I have cleaned it and put a bandage again. What should I do? Should I take her to a clinic? or Some type of specialty doctor? Please advise me? Her health history is Alzheimers, Diabetic, Cirrhosis of Liver due to Heart Failure.