Lightheadedness at 30 weeks?

Hi. I’m 30 weeks pregnant and the past few days whenever I get myself up to do something productive I get extremely lightheaded and suddenly exhausted. It is so frustrating being that I have so little time left yet so much still to do & whenever I push myself to get something done I can’t manage to even complete a significant part of the task. It comes along with a bit of nausea as well and I wanted to know if this is normal and how I can prevent this?