I Am Having A List Of Symptoms And I Was

I am having a list of symptoms and I was wondering if I could get an answer as to what the symptoms may be. For a background: I am a 20 year old female and my fiancé and I are sexually active, for about five weeks I have been feeling sick, it started off with nausea, heartburn and hunger all in one. Then later I was feeling extreme loss of energy, even right after I've eaten and faintness all day long. And now I've I add on the symptoms of weight gain, only in specific areas (my stomach) and no weight gain in any other areas. And I know these symptoms sound like pregnancy and I thought about that, I have the Nexplanon injection, and I took a pregnancy test a week ago that proved to be negative. And I was just wondering if these symptoms could add up to anything else, or if there is a possibility that after a test I could still be just pregnant. An answer would be much help. Thank you.