Why am I so tired

I am almost 29 weeks and today after I woke up from a 9 hour long sleep I ate and went to a garage sale and went with my husband to get his hair cut and then came back home only to nap on and off from 1230-3. I can sleep as much as a toddler if I was off every day. Why am I always so tired. Is anyone else this tired in the 3rd trimester.