Think about it, a little dude is nestling down inside of you trying to situate him/herself for a nine month stay. You can't help but feel a little burrowing going on. It is happening to one of your organs for goodness sake :) I definitely would not worry about a little cramping. My RE always says they WANT your pregnancy to feel a little like your period is about to come (but of course it never does). Congrats!!!
Cramping is really normal and very common in early pregnancy. Congrats on your pregnancy!!
I know that with all of my healthy pregnancies, I always had very slight cramping for quite a few weeks. Sometimes it can be your muscles preparing or implantation "stuff." I did have a m/c with my third pregnancy, but oddly I only remember cramping with that pregnancy in my 9th week when the m/c began....and a great deal of the cramping was in my back.
I'm sure what you are experiencing is just your body preparing for the little bean=) Congrats, and best wishes!
Congratulations on your BFP! It's really too early to predict if this pregnancy will "stick" - but I hope it does! Mild cramping really never "means" anything, but I understand how it can be worrying. Best wishes!