What Causes Swollen Red Finger With Pain In Arm?

I have this swollen, red/purple index finger, and this underlying health problem i have a compromised immune system iv tried to treat it at home but oh my, its so pain full!! i can feel my pulse at the tip of my finger sometimes i can feel nothing like i have no sensation in it. my finger is very hot and my hand feels like it getting hot flush, im taking painkillers and anti inflammatory for this because its that sore, I also have some pain in my arm too. any advice?