3 missed periods neg tests! whats going on?

It's good your going to the doctor, print out your list of symptoms to bring and show the doctor. Ask your doctor to give you a Blood test for pregnancy; it is more accurate than urine pregnancy tests. If the Blood test comes out negative you can ask for an ultrasound too. Some of your symptoms sound like IBS and some symptoms sound like pregnancy and some of the symptoms sound like neither. I'm glad you’re going to the doctor to get checked out. Good Luck!