For Approximately 24 Hours Now I've Had A Red Rash

For approximately 24 hours now I've had a red rash over my extremities, stomach, and back. Not itchy, not raised, does not look like hives. No changes in lotions, clothing, detergent etc. The rash blanches with refill at approximately 4 seconds. Ive taken benadryl without any relief so evaluate if this is an allergic reaction to something. The rash will fade slightly then come back bright red and it actually goes up on my hands to my first knuckle. I've also had a cough with some yellow sputum. With the rash, i've noticed joint pain in my left hand and now the joint pain is in my right hand, predominately in my ring finger/pinky finger on the lower knuckles. My chest on the right is also hurting along with my shoulders. Can you offer me any insight?