It could be a nerve thing... Baby pinching off a nerve? I had sciatica when I was pregnant and my butt would go to sleep sometimes - lol. It was accompanied with tingling and shooting pain, but only when I was REALLY pregnant. At the beginning it was only the numbness. However, I'd at least ask... You should have an appt. around 20 weeks, right? I'd think it would be fine to wait until then as long as things don't get any worse.