In biology, cell theory is a scientific theory which describes the properties of cells. These cells are the basic unit of structure in all organisms and also the basic unit of reproduction.
The three cell theory's are:
a. Cells are the smallest unit of life
b. All living organisms are made of cells
c. All cells come from existing cells
Here are the definitions of unicellular and multicellular organisms
Unicellular: made of one cell
Multicellular: made of many cells
So unicellular and multicellular are two different things in your body made up of all different types of cells.