Hi thanks for your question.
Don't' worry and be relaxed.
The pea sized lump which your mentioning on your labia majora
could be eigther folliculitis
or small lipoma
since it has decreased in size the possibility is more of folliculitis.
Wait for 2 to 3 days,if it doesn't subbsides of its own, take a course of atibiotic for 3 days .Hope fully it will subsides of its and will not need antibiotics.
Hope I answered your question.