As a result of hormonal changes during your menstrual cycle, your vaginal discharge can vary in its appearance and nature accordingly. During the pre-ovulatory phase of the cycle, the oestrogen levels are low and the discharge is thick and sticky.
This forms a mucus plug which blocks the cervical canal and can potentially make it hostile to sperm. Once your fertile period approaches with the rise in oestrogen levels, the discharge becomes wet and slippery like egg white.
As ovulation occurs, the discharge is then more fluid and thinner which helps protect sperm from acidic secretions in the vagina and keeps sperm alive to aid sperm migration into the uterus. Following ovulation, the discharge again becomes thick and sticky preventing sperm entry into the uterus. your vaginal discharge therefore helps your chances of conceiving during your fertile period.
This is the variation in vaginal discharge during your normal menstrual cycle. A yellow sticky discharge therefore may not be physiological ("normal") so it is best to have this checked out to exclude vaginal infections which may possibly damage your Fallopian tubes and therefore your chances of getting pregnant.