Well, if you feel unhealthy, there are plenty of things to do. Otherwise, different people are attracted to different types. If that wasn't so, we wouldn't have the diversity we see in the various people we run into every day. Having been both clinically underweight and clinically overweight in my lifetime has taught me that there is *always* someone who will find you attractive.
If you want to change yourself for your own reasons, go for it, as long as you don't neglect the whole health thing. If not, don't bother. Just be happy.