Scared to death!

My boyfriend came on my lower stomach in the shower. This happened 8 days ago.  Any possibility I could be pregnant? I think some of his ejaculate was near my vagina. At least that's what it looked like. My period starts the 6th. I'm a virgin. My boobs are sore and hot. I think my nipples are darker. I'm constipated. I have been stressed and worried sick. Today I took a test and it was negative. I've read that this can cause pregnancy and I've read that it is nearly impossible. Please help! These symptoms started 4-5 days after. Am I pregnant?!