I had my Mirena for 7.5 years. (got first after I delivered my second child, and swapped for a new one at the 5 year mark.) Removed it on April 1st, found out I was pregnant on July 4th... Same symptoms: sore/tender breasts and nipples especially, and nausea with no vomiting. I am now 23 weeks. Don't discount any possible symptoms, because it is quite possible.
I'm 19 as well and a FTM. I had very sore breasts which I never had before getting my period and more painful cramps than I usually get before I started. It could be a possibility! I would wait a lil' longer closer to when your supposed to start and then take a test.