When you create a post or question there is a thin beige line just above the entry field, it has a small downward facing triangle on the far left of it.  Click that triangle and you will be shown some options including a font size selection.  See if changing that font size makes your text readable, and if that works please try that same method on a few different areas (journal, forum, private message) and let me know if you are having to set the font size each time.