HI,Dear, Thanks for the query from you for  pea sized lump on inner labia, which was tender,red,without whiteheads etc,which vanished lately.1-I feel concerned that you are serious to know why this 
labia minora lump had grown n vanished lately ?2-In my opinion this  inner labial lump is infected sebaceous 
cyst,which was drained in turn.3-You should not worry for the 
STD as its cause ,but a test may be needed if your ER doctor feels,after getting more details from you.4-Hence I would advise a 
second opinion from a  gynaec specialist   who would do -CBC etc.This would give lead on your  worry  which you expressed about labia minora-lump.  4-a-A drug trial with proper antibiotics, would resolve your worry,by clinical trial also.5-Hence I would advise ER  gynaec-  Surgeons opinion.Hope this would resolve the causative worry of the patient in question 6.If treated on this line, the fearing patient , should not worry you much.7-Hope this would solve your worry of the lump  outside labia minora.8-Wellcome to HCM for any more query.