False negative pregnancy test?

Patient: I have irregular period and i had sex 19 days ago, we used withdrawal method and he pulled out long before he came, but I’m still concerned if I could got pregnant. I took a test today’s morning and it was negative. Can it be false negative results? I have experienced cramps, tender breast and nausea during the last couple days, but i also have stomach problems, and i’m pretty stressed out of idea of pregnancy, so it’s confusing to know for sure if it was pregnancy symptoms or symptoms of any other thing. Please, help me!

Symptoms: Cramping, nausea, diarrhea, tender breast