HELP?! COULD I GET PREGNANT OFF BIRTH CONTROL?

I am 20 and on Nexplanon (arm implant). I have been nauseous the last 5 days, and have had headaches on the left side of my head. My stomach is also kind of bigger, not saying it is a baby. I weigh 5ft and 106 lbs, and still do. But my stomach has been like this for 4 days.. My boyfriend and I both got STD tested and came back 100% clean so he ejaculates inside me every session. As you can see on my calender, it is a lot. I also had a period at the end of March. Could I possible be pregnant..? Is that even possible? I asked my doctor to pregnancy test me and she said I most likely don't even have to because it is almost impossible on Nexplanon so I just took her word for it and canceled my appointment... I was super naousous this morning and am scared. I am on vacation currently and cannot find a pregnancy test.