If you recently started exercising again, 45-60 minutes of activity is a lot and could easily be contributing to your fatigue. I'd recommend starting with 30 minutes or so (which could include both cardio and strength training), 4 days a week and see how that feels. Also make sure you're tracking your food regularly. If you're falling short on your calorie goals or any specific nutrients (like iron), that can also be a factor in how you're feeling.
If none of that seems to be helping and the sleepiness continues, I'd recommend talking to your doctor about it.
Hope that helps,