Same thing happened to my DS (very red tip but no noticable discomfort) and it turned out to be thrush. I initally thought it was some kind of nappy rash and just tried nappy rash cream for a day or so but it didn't get any better, so we took a trip to the doctors! Apparently a nappy is a ideal place for thrush - wet and warm.. (ewww). The doctor gave him a few creams - I think one was a thrush treatment and the other was a cortisone cream for any pain and it healed very quickly and hasn't returned.