To know how to deal with it, it's important to know what it is from. I haven't heard of many bug bites from mosquitos in that area, so I would probably say that is not likely the cause- however it could have come from your swim suit rubbing up against the area causing an irritation. At this point, I would just make sure you keep the area clean and don't pick at it. If it doesn't start to look better, or it gets worse, you may consider having a doctor take a look to ensure it's not infected.