I.S.
M., When I got pregnant many years ago I had those same period like symptoms, cramps, back pain and breast tenderness. I don't recall how some after I took a pregnancy test but it was VERY soon after. With that pregnancy I wasn't in a place in my life to have baby and had an abortion.
I became pregnant in September 2007, my OBGYN did a pregnancy test and it was positive, I was ONLY two weeks pregnant at the time. So, I would say if it's been two weeks to a month since you had intercourse I'd go ahead and take a test. You can always try those early detection tests.
Best of luck.