Yes, it can last one day and be light. Changes in your body may reflect in your period. Did you start Birth Control pills? A diet? under stress? new exercise routine? sick? Any one of these can change a period. Your age can make a difference. If you are young and just starting a monthly cycle it can take as much as a year before it will "settle down" and be truly on time and accurate. If this continues call your doctor just to make sure that there is nothing to worry about.
All home pregnancy tests*
I am two months late and i have taken a test sometimes twice a week and they say negative. what is going on?
there could be many health related issues with that you should contact your doctor.
pregnancy test could be wrong. try a more accurate one
Malnutrition
Pregnancy
yes
No you can't be pregnant and still have your period. You can have a light bleed but not a period. As for the whole negative test thing, it could be a false negative.
If your pregnancy test was negative, you got your period and your breasts are sore it could just mean that they're growing. Breasts can also be sore or tender during your period.
There are many reasons why a woman won't have a period. Your weight could be too low, you could be taking medications which will stop your period (like narcotics), you could be in menopause, you could be heavily into sports or exercise. The most important thing for you to do is go to your doctor to discover why you have stopped your period. There are many medical conditions with cessation of menarche as a symptom, and all of them require that you be seen by a medical doctor. If it's been six months since your last period, you are about four months late in seeing a doctor. This is not a symptom you need to ignore.
You could by a small chance, but, you might also imagine the symptoms (phantom pregnancy). Or your pregnancy is too small at the moment. Try testing again in a week or two (when your period hasn't started). If still negative and you got the symptoms and no period then go see a doctor.
There are several reasons for not having a period, but namely pregnancy. If you have not had your period in over 3 months, that would put you in the first trimester. The best way to check, is to get a pregnancy urine test at your local pharmaceutical store.