Missed Period

OK in April my period was late but finally came on a week later but was really light and pink. May came and gone, No period. Here it is June and I've just had a little spotting here and there. Breast tender and always tired but I've taking 3 pregnancy test, two from the store and one at the doc. All 3 came out Negative. But I've had two other pregnancies in the past, which they never caught doing a urine test. Im guessing they just got to draw blood or do and ultrasound. I'm not sure at the point