Why do i wake up sweating?!

I’m 5 months pregnant and not showin that much. I’ve gained less than 20 pounds so I can’t even say it’s the extra weight. Every night I go to bed I wake up sweating. I have the Ac at 74. Last night I was so hot I put it at 72 and my fiancé said I had it freezing in here and i still woke up sweating. I use to always be cold now i’m always hot, only when I wake up and super thirsty and drink so much water as soon as I open my eyes. What is the reason for this? Any advice?!