You don’t say how you are aligning your paragraphs (I learned a long time ago not to take anything for granted when helping to solve someone’s computer problems) but if you are clicking on the appropriate alignment button in the toolbar to align your paragraph left or right, then understand that this command changes the entire paragraph.
If other “paragraphs” are also changing alignment, then that is an indication that the other paragraphs are not really separate paragraphs; they are part of the same paragraph.
If you are somehow just adding spaces until new lines appear, that is not a new paragraph. Typing the “enter” or “return” key while holding down the Shift key creates a new line, but not a new paragraph. Word distinguishes a new paragraph by hitting the “enter” or “return” key by itself. A quick way to tell is to click on the “show/hide paragraph” button on the toolbar, the button with the styalized backwards P. Each new paragraph mark will show up as that same backwards P symbol at the end of the paragraph, whereas hard returns (new line but not a new paragraph) will show up as a hooked arrow symbol pointing to the left.
If this is not it you’ll have to look for another cause, but this would seem to explain your senario.