Help! I'm trapped in an old woman's body!

I reached a new stage in pregnancy this week, the I'm-so-tired-and-out-of-breath-without-even-doing-anything stage. I get so fatigued all the time now! Here is an example of what I mean: Yesterday Jason and I decided to walk to Shopko. By the time we got there, I was so tired I had to rest on a chair in the patio furniture display section before I could begin shopping for anything. Then, after finding what we wanted, I had to rest again before leaving. On the way home I had to stop every few yards to rest...I felt like I had just run a marathon! It got really exciting when Jason was practically carrying me across a parking lot and I almost passed out. My vision got really blurry, I felt really hot, and my legs stopped working. Jason got me to a grassy parking strip where I laid down while people stared at me while driving by. Jason ran home to get the car because I knew I wouldn't make it home otherwise. I was so happy to be home, and so happy that Jason was with me! I guess I really need to be careful about how much I exert myself. Also, my balance it suddenly way off. Today I was doing a little weeding in the back flower beds, and when I stood up, a lost my balance and fell on my bum. I tried grabbing the weed bucket on my way down, but, oddly enough, it didn't stop me from falling. Wow, being pregnant is such an daily adventure!