What Causes Missing Periods, Abdominal Bloating And Tender Breasts?

Hi, I have had sex 7 weeks ago, last week I started getting what I thought were symptoms of pregnancy? Such as abdominal bloating, lower back pain, fatigue, missed period, breast tenderness, and frequent trips to the bathroom.. All that makes me think I'm pregnant, and then when I pee it burns at the end, and when I stand up I have to pee again, but I can't, that's the only think that makes me think that all of these symptoms are something different..