This is actually a possible hernia. You state that one side of the teste is lower than the other...
Question for you: Do you see a big lump on one teste? If so, can it easily be pushed inside your body? If this is true, you are most probably experiencing a hernia.
There are medical procedures that can eliminate the hernia, and they take a few hours to complete (the surgery it self)
This wouldn't be due to an std, and you would get many more responses in the men's health forum.
Aj