Bump in inguinal area, bubble-like, feels sore. had this before but went away and now it's back. how do i treat it/what is it?

See your OB/GYN: I encourage you too see your OB/GYN. What you describe may be a Bartholin gland cyst. However, a young woman should start to see their OB/GYN around 21 and get a Pap smear and screening for STDs in line with the United States Preventative Services Taskforce. Soak in warm water and try to drain and see MD. Good luck. https://www.nlm.nih.gov/medlineplus/ency/article/001489.htm