It is hard to answer this question without knowing what kinds of sickness you have been having. Generally speaking, vitamin deficiencies are not a major cause of frequent illness
, although in some situations this can happen.
If by 'getting sick a lot' you mean that you have had frequent sore throats, colds, and the like, then this is definitely not due to a vitamin deficiency. Although it is commonly thought that taking large amounts of vitamins such as vitamin C can prevent common colds and other simple infections, this has never actually been demonstrated to be true.
An the other hand, what is true is that is that certain occupations are at a higher risk of frequent common infections. For example if you are a health care worker or a school teacher, you will be more exposed to common viruses and so you will likely get sick more often.
Certain types of recurrent infections, such as recurrent sore throats or ear infections or lung infections can be a sign of an underlying medical problem or an immune deficiency. However, in order to determine this, you would need to have a full medical checkup with your primary care doctor