I Have 5 Unusual Bruises On My Arm. It Hurts

I have 5 unusual bruises on my arm. It hurts and it makes my arm weak.I also get an unusual rash on it. To me it looks like bruising but not sure. My arm gets very weak.My hand hurts.And on my forearm is swollen with like a cyst knot under skin. I haven't hurt myself so the bruises and pain should not be there.