am I pregnant

Ok so my fiancé and I have been together for a year and 6 months and we've been trying to have a baby now please understand that he is 38 years older than me I'm 20 and he's still going he's been really sick battling with lung cancer and pneumonia well ok here it goes it's not quite 2 weeks yet and I'm already feeling pregnancy signs like constantly tired back pain headaches nausea cramping in my stomach sensitivity to sertain foods and I'm eating foods that I don't even like. 2 days ago I received my period I'm thinking but it's not acting like my period my mom called and asked a nurse if it is pregnancy and the nurse said to take a test so I did and it came out negative but I'm still getting all of these signs so what could it be if you have any suggestions please feel free to share I can really use the help thank you