Congratulations on day 13! I'm 5 days ahead of you!
I've noticed I get very tired at night! I used to stay up until 12am or so every night and get up at 7, not I'm starting to doze on the couch at around 9. At the same time though, I've felt better exercising and have had more stamina to go on long walks. I think everyone is different. You might want to see a doctor if you continue to feel off. There are a lot of things that can cause your symptoms from detox to a vitamin deficiency to an illness.