Cramping at 3dpo?

So I know these aren't pregnancy signs already as I'm only jut 3dpo. But I keep cramping. It's not bad but it's uncomfortable and slightly painful but I can manage if that makes sense. I got a little bit of a backache today too and it was strange because it didn't last long. I also have really sore boobs! Last cycle I got a bfp (chem preg) and my breasts didn't begin to hurt until 7dpo so feel like I could be out already! What's all this cramping mean? Is it the egg moving through my tubes or something?