I Have A 'rash' On Both Shins. Only On My

I have a 'rash' on both shins. Only on my shins. I've had it for 2.5 years and I say rash but its not really a rash. I am extremely itchy on both shins. I have seen multiple dermatologist's with zero luck. I have had a alergy test and I am not alergic to anything. They finally did a biopsy on one of my shins and there is an excess of blood there. So the thought was that I might have resistance however they have done several ultrasounds and only found minimal resistance in my right leg which should not account for the redness and itchyness I have and zero resistance in my left leg. It looks awful. VERY red splotchy and extremely itchy to the point I scratch it until it bleeds. I have heard from multiple doctors Im a medical mistery. Any thoughts on what this could be would be extremely appreciated.