Groin pain - or pain in the bikini line as you are describing - is a very common complaint. It has a range of causes, some of which can be serious. You should talk with a physician about this pain that you are having, but be prepared to discuss some of the following conditions.
The most common cause of groin pain is a strained or torn tendon, ligament, or muscle. There are a number of structures in the leg that attach at the groin, and these can be injured either through overuse or acutely in overexertion. These types of injuries tend to improve on their own over time, but if yours persists despite rest, it is recommended that you see a sports medicine doctor
or an orthopedic surgeon
If your pain is associated with raised red bumps or irritation around your hair follicles, you may have folliculitis. Folliculitis is an infection of the hair follicles with either a fungus or a bacteria that can lead to soreness and itchiness. It commonly occurs after being in a hot tub or if you shave this area with a razor, but can also occur spontaneously. Folliculitis may resolve on its own, but if you do notice a persistent rash, you should see a doctor.
Another cause of groin pain is an enlarged lymph node. There are many lymph nodes located in the groin, and when they are enlarged, they can be painful to the touch. An enlarged node would feel like a round, rubbery or hard mass at your groin. An enlarged node can be a reaction to a local infection, but can also be a sign of something more serious, like a cancer. If you can feel an enlarged node, it is best to have it evaluated.
An inguinal hernia is a hernia that occurs in the groin area. If your pain is due to a hernia, you would likely appreciate a palpable bulge in this area or redness of the overlying skin. Inguinal hernias are much more common in men than in women. If you feel you have a hernia and it is bothering you, you should be seen by a general surgeon.
It is not possible to diagnose the cause of your groin pain without being evaluated by a physician. I strongly advise you to see your primary care doctor
, and (if necessary), be referred to a surgeon, sports medicine, doctor, or other specialist.