How to prevent a yeast infection?

Ive been dealing with yeast infections on and off for years (ever before i became sexually active). they usually clear up on their own but i just recently got rid of one using an anti-fungal suppository. wat can i do to keep them from coming back. i bathe frequently, once or twice a day washing only with plain white soap like dove or ivory, i dont douche or use any other feminine products. i do use tampons from time to time during my period but i alternate between pads throughout the day. i dont wear tight underwear at night, i usually sleep n male boxers or just loose underwear. so i dont kno wat i could possibly b doing wrong from them to keep coming back. is there anything i can do to eliminate this problem for good???