I am 25 years old and a few weeks ago i started experiencing nausea,headaches, fatigue, cramps, emotional, gassy, my breast were tender, and a full feeling below my stomach. in about a month i lost 13 pounds because i couldn't i was to nauseous to eat. I went to the doctor and i had a pregnancy test about a week before my period was expected to start. it was negative. they said it was most likely PMS and would go away once my period started. i don't normal have severe PMS if any at all. the week i was due to start my period i was told that i had chlamydia and went in to get treated. my period ended up being almost four days late. bleeding was not normal(lasted three days extremely lite) and ended abruptly. i went back to the doctor today because i am still having cramping(that worsen when i have to pee, but no pain or burning with urination), low back pain, fatigue, headaches, breast tenderness that comes and goes. they couldn't really give me a reason why i am still feeling this way. i had a period so i know i cant be pregnant, but i know something is definitely wrong. what could it be?