Fertile cervical mucus lasts for 5-7 days starting 9 days after period -- still nursing son. could it just be nursing causing this?

Unlikely: I don't know how long ago you've delivered, but the fertile mucus suggests that you're ovulatory. If you don't want to conceive i suggest using barrier contraception.

Normal mucus: Ripe cervical mucus can be noted 1 -7 days before ovulation. This transparent raw egg white like fluid is normal as you describe. This is not related to nursing and is probably normal.