Other than Pregnancy, what other causes are there for late period?

I am 27 years old, so it isn't menopause. I have 4 children and after the last I had a tubal ligation. For a little over a month I have felt nauseous, have not been able to drink coffee, over emotional, and now I am having some stomach pains, noiting too serious, more uncomfortable (like pressure, similar to what I have felt in early pregnancy before). I am now 5 days late. But I know that becoming pregnant after tubal ligation is not very likely. I am goint to take a test very soon, maybe later today. I was just wondering is anyone knew of anything else that could cause me to ba late, or to have these other symptoms.