I would suggest drink less coffee and eat more iron rich food or find out if you can take ferrous Sulfate really good iron tablets that will help boost your iron stores and iron level. I'm severely anaemic and I'm currently 35 weeks and plan on working till 37 weeks and these have helped. If you can make spinach and kale smoothies as they are high in iron.
This was the time during my first pregnancy that I began working part time. Full time became too demanding and stressful for my body. See if you could cut your hours.. even if it's just one day less it will make a big difference
Your iron is probably low. This happened to me a few weeks ago and my doctor told me I had to get more iron
Here's some advice from the MedHelp website and our I'm Expecting app on fatigue. You can find this in the app by going to the Pregnancy Diary from the home screen and selecting Fatigue from the Symptoms menu. Then click the menu bar in the upper left and select Symptoms Manual to see your symptoms. Hope it helps!
http://www.medhelp.org/pregnancy-health/articles/Fatigue-and-Insomnia-During-Pregnancy-Your-Symptoms-Manual/1986