Suggest Treatment For Swollen,painful And Sore Skin Behind Knee

Hello, I am a bk amputee since I was a baby...I have gotten a sore behind my knee, about the size of an egg. It's extremley painful and I don't know what it is. I went to the doctor and I was seen by a PA and a doctor, both of which were clueless on how to treat me or even what it was. They shot a needle in and tried to get something out but only got blood. Since then the swelling isn't getting any better and I haven't been able to wear my leg for 6 days. They called it a hematoma and sent me home with antibiotics. My question is, do you think I should go back to the doctor? How do I treat this painful pressure sore/boil/mysterious swelling? I've tried cold, heat, soaking, elevating...I'm really at a loss. Can you help? Terri Vancouver WA