Unknown Allergy Diagnosis: Rash Underneath Skin

I recently been diagnosed with an unknown allergy. I breakout with a rash that is underneath my skin. I took allergy tests and nothing was pronounced in the test. I also took a blood test in hopes it would gives us an idea what is causing the rash which is vey uncomfortable, burns and hurts along with itching. The count was high but could not identify the source of allergy. Dr prescribed Doxepin so I can sleep better at night due to itching. I still have the itching and rash but not as unbearable.