Did your doctor check you for vasculitis?
He would have done an ANCA, ANA, C-rp, Rheumatoid Factor and ESR(erythrocyte sediment rate) for vasculitis.
Some are ANCA negative, but still have vasculitis which commonly attacks the kidneys and lungs and a kidney biopsy is the only way to positively diagnose.
Red spots like rash on the legs, arms or body are also, common.
I would suggest that you get those autoimmune panels done because vasculitis can destroy the kidneys in as little 3-6 months.