anyone else?

Anyone else struggling to do the things that always were a breeze before? I'm 30 + 5 and literally can hardly do anything before I have to sit down before I fall down! Thought I'd clean the kitchen, all I've done is take a few bits out of a cupboard, washed up and wiped the surfaces down...I'm now sat on the sofa chugging down water to make myself feel better! I had my routine bloods done at 28 weeks and they called me last week to say that my iron levels are very low so I'm now on iron tablets. They also said b12 and folate levels are low and that I have too many anti bodies in my system from being rh neg blood group (I've had the injection) could any of this be why I feel like this? Or is it just common now in the third trimester? I never felt like this when I was pregnant with my son 6 years ago!