Gets Easily Tired.

21 weeks now and I realized that I easily get tired just by doing small stuff. Like walking at the mall, doing VERY FEW laundry, doing groceries, etc. Is it normal? I am a first time mom and I am already 32 years old. I kept on thinking that my age might be a factor why I feel tired most of the time or my body is too weak to be pregnant at this age. Is there anything that I can do to lessen my legs and back pain at night? Thanks!