What Causes Blurred Vision And Dizziness During Pregnancy?

I am in my last trimester of pregnancy and over the last few weeks I have been experiencing some things that have left me scared and concerned. At random times I will get hot and very fatigued, and then my vision will blur out like someone is dimming the lights and I will then see dark spots until it comes back little by little, my hearing becomes muffled, I get nauseated, and feel like I am going to faint. Usually this will all last about three minutes or so then I will feel okay, but it will leave me extremely weak and fatigued the rest of the day and even getting up to use the bathroom feels like a work out. I am eating and hydrating well and when I had blood work and glucose screening done a few weeks ago it all came back fine. I had a slightly low hemoglobin level but it is easily managed. I know when the baby sits on your vena cava it can leave you with these symptoms, but it has happened sitting, standing, laying on my side, while showering, and each time I was not in the middle of activity or sleep/nutrient/hydration deprived.