How can I make my body less frail?

I am a female university student who works hard. I also have a part time job. In my opinion, I do not push myself a lot harder than any of my friends. However, I feel like I get ill all the time. My body doesn't seem to be able to cope with my lifestyle as much as other people my age. I am underweight but I eat healthily, don't drink too often and don't smoke. I also do not eat a lot of meat as I don't like it. Is there a way I can make my body able to cope with more, such as taking more vitamins, particular excerise or eating specific foods?
Thanks for your help

Hi! You should probably see a doctor first, to make sure that nothing that would need medical attention is going on with you.

Hi guys,...
I think using of fitness exercises and stairs as compared to pills are more beneficial for losing weight and maintain health and make body perfect,..

regards,..

I agree with you Shawn,..
Pills have side effects so exercise with diet combined is very well,..