What is going on

Im on nexplanon for about four months now. But every now and then i have headaches and stomach pains. But about two days ago i have been having really bad head pains i feel nauseous and i cant eat. i looked it up and it says i may be pregnant but im not sure if I can be because im on nexplanon, my doc said its over 99 percent sooo im a little worried. i have made an appointment but it wont be till another month plz help!