EXTREME Tiredness WTH???

Bree • I`m 27 yrs old and have one son (8). I just had our second. Not sure if we're done or not.
Usually I can stay up pretty late with no naps and have energy to do something. I'm 6 wks. And the last two days I have been at work and my eyes are literally trying to shut on me. I'm that tired. I work at our local store so I move around quite a bit. I'm also trying to eat healthier. Any ideas?? I don't remember this with my son.