Swollen Penis

24 hours exactly after having what I will call a vigorous sex with my Girl friend whom I trust, I felt a mild pain on my groin both left and right and that it was swollen. The pubic hair area was swollen too all to my penis also swollen. But my scrotum was not swollen. A mild pain of swollen. I can run, walk and sit with no pain. I took a tylenol that night and went to sleep. The next day it subsided a bit and by the third day it was all gone. I asked her if she had it with somebody somewhere and she denied. I didnt go to the doctor but I didnt have sex again and its been a week now and I am still wondering what that could be.What kind of STD is that? If that was the case. Got me thinking so bad I don`t wanna have it no more till I figure out what this is.