HELP! Pregnancy, Early Menopause, or Stress?

What are my chances of being pregnant, early menopause (im only 21), or stress causing my [now] 2 missed periods. My last period was 8/7/2010, and my boyfriend and I have every night. Its not like we are trying to have a baby, but if we do, were ready for it. (he already has a 3 yr old [my step-daughter] that i take care of everyday, so do not try and tell me i am too young, or how hard it is, cause we already know) Anyways, i was spotting 2 different times and little cramps but nothing bad [once on 2 completely different days, about 2-3 days after the first time is when the second time occurred] about 2-3 weeks after my last period. My are sore, ESPECIALLY my right one, and has been for a while. I have nausea, but mainly at night, so its not really morning sickness, at least i don't think. My boyfriend says i have a better sense of smell and i crave certain foods, but i don't notice that. I have gained a little weight, and i do get dizzy sometimes, but i don't know if dizziness is a pregnancy symptom.... anyways, i know some of these relate to everything in a different way of Pregnancy, Early Menopause, and Stress.