XP: Cramps

Millie1984

Sorry if this has been posted already, but this is my first pregnancy and I am just trying to figure out what is normal and what isn't.  

I am 4 weeks and 5 days and today for the first time I am experiencing cramping.  I know other people on here have experienced cramping as well, but what I don't understand is why.  I know there is some cramping upon implantation, but isn't the embryo already implanted at this point?  Thats why I got a positive pregnancy test?  Is cramping really normal, and if so, what is causing it at this point?  

I am SO sorry if this is a stupid question (or if this was already answered), I just need a little piece of mind right now...