Brief Answer:
See below
Detailed Answer:
Hello, I'm Dr. Branch, thanks for using Ask a Doctor. There are many possible causes for a late period, including stress, and it can be normal for periods to vary from 21 to 35 days. Even if you missed one period, it wouldn't necessarily be important to investigate why. However, the first thing you would want to rule out is pregnancy. If there is any chance you are pregnant, I would check a pregnancy test.
If you are not pregnant, then it would be safe to wait. If you missed your period for 3 months or more, than you should be evaluated for causes of this. Your doctor would likely want to check your hormone levels, including your thyroid, and possibly get an ultrasound to look your uterus and ovaries to look for polycystic ovarian syndrome or scarring inside your uterus.
Cramping and nipple tenderness would suggest pregnancy, so I would make sure to check for that. Thick white discharge, especially if it is associated with itching, may be from a yeast infection, so I would suggest using clotrimazole cream once daily inside the vagina for 7 days.
I hope that helps, please let me know if you have any other questions and I'd be glad to discuss it further with you.