I don't think it's hiccups but I guess it could be I looked it up late last night and I had no idea they started this soon it was so weird it's been five years since my last one so it's like experienceing it for the first time all over agin

It could also be the baby head down

Braxton hicks can actually start as early as 12 weeks. We usually just can't feel them that early. But yes, you can feel alot of pressure that early too. It all depends on how baby is sitting. My children like to sit very low with their heads in my pelvis so I constantly feel pressure and it makes it difficult to walk. As for the pulsating, is it possibly hiccups? Or do you feel those too.