Can they go away by themselves?

I unfortunately get them all the time without symptoms..anyway they dont go away on their own you will need antibiotics like Bactrim and its best to take Diflucan too when your on the bactrim because the antibiotic will probably give you a yeast infection.

Common Symptoms are:

Strong Smelling Urine
Cloudy Urine
Lower back pain
Pain when urinating

Symptoms of a bladder infections:
Urgent need to urinate
Frequent urination
Burning or pain during urination (dysuria)
Bladder spasms
Cloudy, bloody, or foul-smelling urine
Pain in lower back or abdomen
Pain above the pubic bone
Shakiness and fatigue
Mild fever

Bladder infections do not go away by themselves.

In case you have a bladder infections or not here are some treatments of bladder infections:
Cranberry Juice
Prune Juice
Antibiotics
Over-the-counter drugs (painkillers, anti-inflammatories or antispasmodics)

I hope this helps.
P.S.
I know you did not ask for my last paragraph but just in case you were just curious.