I have an office job and during my first trimester I was always so sleepy in the afternoons (after my lunch break usually) I found that taking a short walk around the office or up and down the stairs a couple of times helped me. Though it is hard to get yourself motivated for activity when you are already so tired. But it kept me from falling asleep at my desk. Good luck!
I feel you... I'm constantly sleepy... Struggle to get through the day without a nap.. I didn't find anything to help it... Just waiting for the third trimester to arrive , they say you get lots of energy then
Rest or sleep when you can. Listen to your body and take more breaks than usual. Otherwise, you just kind of have to ride it out. It will get better.