Cramps, brown discharge but no period for seven months?

i am 16 years old and have recently become ual active about 4 months ago. i haven't had my period for 7 months though. i get a light brown discharge every now and then but it only lasts for one day. iTook 2 pregnancy tests both negative... what should iDo? iDont really want to tell my mom about me being active. she wont be mad she will just ask a million and 4 questions about when where... how did it feel? ETC. should iGo to a doctor or what?