Annoyed about sleep

I am almost 18 weeks and I'm getting really frustrated because I'll be exhausted, then go up to bed and not be tired. I read for a while in bed then we turn the lights out, and I just CANNOT fall asleep. I tossed and turned until 2:30 last night. Then I left the bedroom and tried to sleep on the couch.

The extra annoying thing is, I set my pillows up the same way as I did the previous night and I had the best sleep of my life and woke up cheerful and happy. I didn't fall asleep til almost 4 in the morning this time so I am NOT cheerful today.

I don't know what it is! I can't get comfortable and I will lay there for hours and my brain just won't turn off...

Somebody tell me the secret 😭😭😭