uterus height at 12 weeks?

So this is TMI, stop reading if you think masterbation is yucky 😜
I'm 12 weeks and had a little fun this morning and my tummy got hard almost up to my belly button when I experienced bliss 😂. I googled and it says my uterus should just barely pop above my public bone.  Why would it get hard so high up? This is my third pregancy. 
Thanks!Â