Well Wombat..I'm glad you asked!
By testicle Infection I assume youre talking about Epididymtis?
Epididymtis is an infection or inflammation of the epididymis, which is a firm tube that lies on the back surface of each testicle. It is coiled in order to fit a length of nearly 20 feet into a small space. This long length acts as a storage space for the sperm and gives sperm time to mature...Inflammation occurs when your sperm is slow and has reached old age by the time they get there and you get clogged by all their tiny little walking stcks and motorized buggy thingy's causing a "traffic jam"..think massive sperm pile up. But its probably infection in your case as I bet your little titans are sprinting that 20 feet clad in Nike's, with teeny weeny little heart rate monitors on and doing it in record time....maybe they have a competition..MAYBE they have "The Sperlimpdicks" with champs like Cathy Foreskin and Porn Frazer and....oh sorry, where was I?
The cause of the infection are usually the same organisms that cause chlamydia (responsible for nearly 50%-60% of cases) and gonorrhea. The bacterial species are Chlamydia trachomatis and Neisseria gonorrhea respectively, this isn't to say you HAVE these STD's..unless you've had unprotected sex with Damits mum lately...its just the batcteria that forms both and are treated by strong antibiotics.
Some pics to help you understand -

I'm sorry...in order to give you the most accurate advice, I need to make this more applicable to you....tiny

(image fixed) -

There is a 3rd strain of bacteria - Chalmydia raginmongrelis, this is brought on by repeated masturbation to Chalmela and is sadly incurable -

As antibitoics are expensive and ultimately just an anti bacterial my recommended treatment is to fill a large vessel with dettol and masturbate with your "tiger" fully immersed in dettol..yes it stings, yes the burning feeling is normal and the blistering is ok, ..but eventually the dettol will make its way down your urethra (cock) and attack those little bacterial bastards with zest.
As a trained medical proffesional I am obligated to warn you of some mild side effects that include the following -
* Pissing napalm for a week..no srsly..napalm, the dettol will mix with urine and sperm and shoot out a flammable sticky substance, you've been warned
* Voice will raise 19 octaves and be able to shatter glass at a single pronounced vowel as its so high and dogs will flock to you en masse and hump your legs clean off.
* Will exhibit a John Wayne type walk as touching your testies together feels like a chinese 1000 needles torture technique
* Possibly develop a type of super power where your cum will eat thru 5 ft of reinforced steel in seconds
* Your cock may begin to disolve from within
and you may get a runny nose
Things like that...nothing too extreme.
If it turns out that its not an infection and you DO have an STD, you need to tell your parents...They'll be shocked and horrified, but if it gets too bad just point at your sister or something and say "Blame her..she fuckin gave it to me!" ..that'll shut em up right fast.
So there ya have it, cause, effect, treatment...please note that if pain persists or you develop any of those side effects, blame your original GP..its not my fault!
Hope that helps,
Chalice M.D.
p.s. Some reference Material (That i wrote during my doctorate) for you to read -
http://www.emedicinehealth.com/testicle_infection_epididymitis/article_em.htmAlso - Yakult (a japanese fermented milk drink found in any supermarket) promotes good bacteria in the intestines and some studies have shown it can prevent some intestinal diseases and bad bacterial build up, which is how you got it most likely via intestine, into bladder and from there..your prob......others say that Yakult is useless, but its been around for 20 years and its claim still holds..it would've been shut down if it didn't do something..check it out and try this as a preventer..having said that I've never had your prob and i'm 33, so it may not happen again..unless its chlamydia from Damits mum, then your fucked.
http://en.wikipedia.org/wiki/Yakult