You should take another pregnancy test. It seems that the brown discharge is simply a minimal spotting - you can still spot blood even after you're pregnant btw.
Pregnancy tests aren't always effective until after you've been pregnant for a certain amount of time.
All of your symptoms kinda sound like you might be pregnant but of course it could always be something else. Stress, worry, etc could make you miss a period and can cause symptoms like that I guess.
Needless to say, take a pregnancy test right now and that should answer your questions once and for all.