Embarrassing problem following surgery

Had a knee replacement four weeks ago. About a week ago
I developed a very small pressure sore which is improving with hydrocolloid plasters but unfortunately I have developed soreness between the buttocks, it's really painful to sit. The GP prescribed antibiotic cream but it hasn't helped, I've bought an anti pressure cushion. Any help and advice would be welcome, I feel as if I will never improve, I know that a bath would help but I can't get into it at the moment.