Is anything bothering you emotionally? That can wear a person down. Is it related to your menses do you think?
Do you get plenty of fresh fruit and vegetables...not canned or dead foods, but fresh? Their are important nutrients in live foods. Also are you dieting? That can affect one's immune system negatively. maybe ina health book or on the internet you can determine a healthy diet or with your parent's help, and see what you acn improve for your health. Clearly something you are doing is amiss here. Do you babysit kids that have sniffles or running noses? That is a common culprit too. I hope you find the source of your illnesses, as that is sure no fun!