Why did my body wake me up?

Amy • First time Michigan mommy to a beautiful daughter, Leila Sky. 26 years young. ❤️🍉🌸🐰🍵🍣🌟🎀
37 weeks along, my body woke me up around 6am... I went to bed at 3am. I didn't have to pee too bad, I had a bit of heartburn, but other than that WHY on earth did it wake me up? I can't fall back asleep!!!! It's my bday, my gift to myself was going to be to sleep in!! Any ideas as to what my body was trying to tell me? Come on man...