What Causes Vaginal And Abdomen Soreness And Spotting?

I had sex with a guy with a large lengthed penis on a friday night, and during the act I felt some minor discomfort with the depth that he was going. On Saturday my abdomen and vagina felt abnormally sore the entire day. On Sunday I noticed a bit of blood rather far up into my vagina but there was no bleeding on Saturday. I'm worried that this could be signs of an STI or maybe something worse. Please help me.