Pregnant Or Something Else ?

I had my period from the 15th through the 19th of last month. A day or two after my period ended, I had unprotected sex. Ten days after that, I began to spot. I started having sharp pains in my lower right stomach and then I began to bleed more heavily. It lasted for four days. It has now been four days later and I have been extremely dizzy, nauseous as well as a feeling of not being able to get full, and have been experiencing back pain and cramps. Also, I don't know if this means anything, it just sticks out in my mind, but it always hurts when I have sexual intercourse . I'm not sure if that's normal or not considering that I've only had intercourse about ten times in my life. I'm really confused as to what this all means. It just seems way too early to me for this to be a pregnancy if all of these symptoms are occurring. Then again, I don't have too much experience in the matter. Can someone please give me some advice. I am twenty years old and do not have any children if that matters.