Have Implanon implant. Experiencing pregnancy symptoms like tiredness, heartburn, constipation, spotting, frequent urination, weight gain, cramps. Reason?

hi. i have the implannon implant have done for 18 months been fine until september missed all periods since (3) i have sore boobs always tired heartburn fell sick (sometimes) constipated eating loads more getting spots which is weird for me and urinating more weight gain look 3 mnths pregnant back ache stomach cramps occasionally but negative hpts and blood had ultrasound and got told she couldnt look for a baby as not why u/s was being done but looked like no baby but she said u/s doesnt show everything so cant be pregnant feel pregnant but whats wrong with me