Welcome to HCM.
It also could be due to recurrence of Genital Herpes
lesions. Sometimes it may likely to appear nearby sites also. Not necessarily confined to the same site, even though quite often it happens in the same way. Due to the color of labial skin and adjacent mucus membrane the color of the present lesions may look odd.
Next possibility is Herpes zoster
lesions occurring along the course of a peripheral nerve
. Here the pain or burning sensation will be more. Apart from these, certain other non venereal blister forming rare skin conditions like pemphigus
, dermatitis herpetiformis
etc. could have occurred.
When you go to your physician he could be able to differentiate these conditions and to offer the diagnosis and treatment for the same.
But there is nothing serious and you will be alright soon.