I weighed 171lb. about 2 months later i'm 163lb(now this morning). i have done nothing and for the past week i've been eating junk food,what is wrong?

See below: you can lose weight on junk food, depending how much you are eating. Do a calorie count of your intake. Also visit your health care professional if you feel you are getting adequate calories and continue to lose weight

Ensure weight accura: Use same weighing scale, early morning weights may be slightly lower than later. Minor weight fluctuations may be normal. Some people may lose weight with stress.

Get good habits: could be different reasons: increased activity? Check your thyroid. Do you feel thirsty or urinating too much? Talk to your doctor as weight loss could be a sign of a serious disease. Finally, get good eating habits early in life, exercise regularly.

Check everything!: Involuntary weight loss obligates evaluation--and the list of causes is huge. Be prepared to discuss symptoms and signs you've noticed over the last 2 months with your provider so he/she can better direct what evaluation is immediately appropriate.