What Causes Delay In Periods And Headache?

Hi my name is Angela, and I'm 26 years old my period always missed a month or two but it's been five months and I have taken five pregnancy test and all came bAck negative. I want to know why is that I weight about 285lbs and I'm 5'3 and I is a little stressed out but try to be stress free please help and also having really bad headaches everyday and last for several hours and I tried everything please help me thank you