i am 100% with tired...i had bad cramps, and lower back pain, i felt exactly like i was going to get my period! doctor said stretching can do that to you...
on a different note - i've had bad back pain for awhile now & finally went in for an mri in november. got the results back yesterday - inflamation in my spine in the middle of the my back & a herniated disc!
i had TERRIBLE lower back pains with my first pregnancy. They kept me up all night. Started the day i got my BFP, and continued for a couple of weeks. My dr said they were completely normal and due to everything stretching and responding to the hormones. you can take tylenol, but honestly, it didn't help much. Congrats!!!
I kind of doubt it is related to the pregnancy this early. It's probably a coincidence. Does it hurt with movement only, does rest help? Or is it there even when you are sitting or lying down? Does it feel like it's in the midline along your spine or is it off to the side(s)? Does it travel into your abdomen or legs? Had you done anything different in the few days prior to when you first noticed it? (wore different shoes, long car ride, carried shopping bags too long, lift something awkward)?