Feeling fatigued and drowsy all the time, especially before dusk. what other tests might be helpful to consider?

That would depend on: What tests you have had, a blood count, thyroid test are good places to start. Do you sleep well at night? Is your stress level elevated, worried alot or having crying spells; must consider a mood or stress componenet; another thing is sleep apnea if you snore badly. There are meds that can help but i would get seen. Can you take a nap during the day if given an opportunity or feel can't nap?