I hadnt gotten my period for a month I know im not pregnant since the results have been negative and I've been spotting brown;what can be the problem?

See you MD. There are many different reasons for missing a period. Your md will ask about your history. Age , medical conditions like thyroid disease and diabetes, life stress, strenuous exercise, and eating disorders are a few things which can affect the menses. A blood pregnancy test may be considered.
Not ovulating . You not having a menstrual cycle (and a neg preg teat) with some brown discharge is seen when you are not ovulating or releasing an egg. This is common. The brown spotting is a small amount of old blood. If you go a few months without a menses, it is common to have a heavy long menstrual cycle after that. If this occurs then you should see an ob/gyn.