please tell me about thrush?

i quit smoking cigarettes a week ago and found out today i have thrush (it hurts me). i have never had this before. does this honestly mean i might have a cancer or hiv or something serious? i have always tested negitive for hiv, i have had 3 kids and been with only one man my whole life. if i tested negative for hiv could i still have it? im so confused and worried about it. could i get thrush from chewing too much gum (i have gone through over a pack a day since i quit smoking) could it be cause from quitting smoking? i was always a healthy person besides the smoking part, so thats why i quit to become healthier. ill be really sad if i find out im sick cause i quit smoking. i really wish i never started smoking, it was the stupidest thing ever!! plz help me out