What Causes Weight Gain,abdominal Cramps And Headaches?

hi doctor i am 24 years old and have a 6 year old son. but lately i have been really tired but i cant sleep i have also sttarted out growing my clothes, i have been having slight cramps in my lower tummy, which has gotten bigger. my last period lasted only 3 days and i have also had a adversion to coffee. i get terrible headaches and i am getting so hot. i did a home preg test which came back negitive. can you perhaps tell me whats wrong with me????