Thank you so much for your question. It is my privilege to be able to help you.
There are many possible reasons for a bump like you describe. Most possibilities are minor problems and will generally resolve on their own with time.
These include labial cysts (occur when a duct in a skin gland gets clogged), infected hair follicles, inclusion cysts (another type of skin cyst),or other things.
They can also be a sexually transmitted infection like herpes or a wart.
If it persists, grows, or becomes very painful, you should see your doctor. If it goes away on its' own, you really don;t need to worry about it. You can try warm soaks 2-3 times a day to see if that helps, as it will often help it go away faster.
I hope you find this helpful. If you have any more questions please feel free to ask me. If you are satisfied, please remember to ACCEPT the answer so that I get credit for my work. BONUSES and positive feedback are always appreciated. Good Luck! Dr. SaulJE