I found this on Net Dr!
Question
I have not had a period for two months, but have taken a pregnancy test which came back negative.
Answer
Yes. Pregnancy tests measure levels of hormones and the hormones rise throughout pregnancy. Sometimes they rise slower than other times. However, that said, the modern pregnancy tests are very sensitive so it is unlikely that you are pregnant with a negative pregnancy test two months after your last period.
The thing to do is repeat it in another month if you still haven't had a period by then. If that is negative there must be some other explanation for your missing periods and you'd need to see your doctor to have it checked out.
The other thing you can think about is whether or not you feel any different. For example, if you are passing urine more frequently, if you feel a little nauseous, if your breasts are feeling different, and, particularly, if your nipples are becoming darker, these things can all be signs of pregnancy.