Cannot Get Relief Of Major Skin Problem Behind Right Knee

Cannot get relief of major skin problem behind right knee of various colors and almost black and blue with a spot in the middle of it that I picked at and since I couldn't see it thought it was a scab but two weeks later and after seeing an elderly physician diagnosing skin rash from sensitive skin, I am very worried and considering the ER. I am a well versed health care professional having made rounds with many disciplines, but not dermatology, Have been using 10 mg Clotrimazole/Betamethasone with no improvement. Have had open-heart at Cleveland Clinic 2 1/2 years ago valve/double bypass. Concerned it is Lyme Disease? Please advise if an experienced medical person see this. Live in Maine where deer ear the hosts in garden!!