13 weeks and more exhausted than before

So I'm 13 weeks and I've come to notice that I'm more exhausted now than in my first trimester. I literally can sleep all day while my son is at school and by 9pm I'm ready to sleep all night, sometimes even taking a nap in between. I wasn't even this tired before. Is this normal? Has anyone else experienced this? I know they say you usually gain some energy around this time but I have yet to. If course everyone is different, just curious.