losing weight.

I eat plenty of food. Still I cant gain weight. My brothers and sisters are pretty plump. I am very much frustrated as I look so thin that even my husband seems to have lost interest in me. More over, my breasts are very lose. It looks as if they were of an old woman. Is there anything that I can do for tightening my breasts?. Can you give me some tips to make myself a bit plump? I have heard people say that eating semen will help. Is that true?. I hope you can help me.