Q: How do I know whether it is semen or cervical fluid?
A: If you find that you have more watery or eggwhite days than you would expect and that these often follow days or nights that you had intercourse, then you may be mistaking seminal and cervical fluid. They have similar properties because they share the same function: transporting and nourishing sperm. You will find, however, that fertile cervical fluid (eggwhite) is more clear and stretchy and shiny. It will stretch a couple of inches without breaking. Semen may be more whitish and is more likely to break when pulled.
If you are in doubt and it is near your fertile time, always record eggwhite cervical fluid, even if it may be obscured by seminal fluid. This way, you will not miss a potentially fertile time. Emitting semen immediately after intercourse by doing kegel exercises (which is sometimes recommended for people who are charting to avoid pregnancy so that cervical fluid is not obscured) is not recommended when you are trying to conceive. While most sperm reach their destination within your reproductive tract quite quickly after intercourse, you don't want to sacrifice your chances of conception to have a perfect chart.