Help!!!!

Im on nexplanon (have for 3 1/2 years, got mine recently replaced in December of 2020). My bf has finished inside of me i think 4 times. I typically am very trusting of nexplanon but Ive been feeling off lately. My lower back hurts really bad and I have pain in my lower abdomen. my joints are also achy. i squeezed my nipples today and some clear dishcharge came out. ive taken 3 pregnancy tests (1 this morning) all negative with no faint lines at all. im so terrified i could be pregnant!! i cannot afford to be pregnant as im in college and it would ruin my life. please if anyone has any advice or has experienced this id really appreciate it. i have horrible anxiety and tend to hyper-fixate on my body when i have a scare.