Fatigue now???

I have been on adderall for 4-5 years, just recently started back on it after a 9 month break for pregnancy. I've noticed after a couple weeks I feel tired like 2 hours after I take it. Not a severe extreme fatigue but the kind of tired you feel when you were busy all day and decide to sit down and chill and the sitting and relaxing causes you to feel sleepy and want to sleep. I'm worried since normally adderall keeps me awake and now two hours after taking it I don't have any problems sleeping. Anyone have this happen??