Implantation cramping! Help?

Hey ladies. I am now 12dpo. Got my BFP on 10dpo. Prior to the BFP I had a few symptoms. These included sore breasts, acid reflux, tiredness, headache etc.
Since yesterday I have been getting cramps in my lower abdomen. It's like a pulling cramp of that makes sense. I know that these cramps could be considered normal for implantation. But what worries me is that it hurts a lot! It comes and goes since yesterday. For example I went to the store today and when I got out of my car I could barely walk from the pain, and after a few minutes it got better. Now it's bad again.
Is this normal? What are your experiences with implantation cramping? Thanks in advance!