Is 4 months post exposure enough to trust a negative blood test? The doctor put me on meds so would that affect the blood work? He just visually confirmed the initial sores whoch were red with a small indent which then turned purplish reddish brownisbh in the centre and scabby and grey almost clear fluid like in the centre preceding the purplish brown centre. Can oral sex with a coldsore cause sores to appear about a 20 or 30 days after initial exposure on my beltline? It doesn't make sense to me why it would appear on my beltline, the doctor didn't care at all so