I'm 24, last month I had my period on the 18th of June it lasted 7 days. This month it came on the 20th of July and only lasted 4 days. I had unprotected sex with my partner on June 25 right after my period was over with. Is there a big chance that I am pregnant or it's just in my head. Please tell me it's all in my head!

I think its in your head... your period can be different lengths of time. Most of the time it is a lack of period that determines pregnancy, and while bleeding can occur, it is usually very light. If you are really concerned about it though, go buy a HPT and ease your mind. Good luck!