I've missed three periods and all the pregnancy test i took are negative , can something else be wrong?

Get checked: Missing 3 periods and neg pregnancy test - rare people need a blood pregnancy test so consider getting that. Most likely your hormones are off and that is preventing ovulation. Most people who don't ovulate don't have periods. Possible causes include weight gain or loss, thyroid issues, prolactin excess, diabetes, eating too much soy, for instance. You'll need to see your doctor to work this up.