Does dieting for too long damage your metabolism

I am a 19 year old female and I have been dieting on and off for two years. I lost a total of 20 pounds and have taken breaks periodically. During some of these breaks I have gained weight. I am planning on losing another 5 pounds but I'm worried that after two years my metabolism will be tired from all of this and losing weight will be much harder.
Thanks in advance!

Replies