Hi, youkali7.
Congratulations on the donation. What you are experiencing is very common amongst donors. Drinking and walking, and power naps, are indeed excellent ideas.
On the other hand, for everyone out there planning to donate: although many many donors report fatigue, to be different

I'll report that I had very little, after the first couple of weeks, when I resumed work. Considering that I have a fairly demanding schedule, I was very fortunate not to need more sleep than the 5 hours a night I was typically getting once I resumed work.
However, I have a long public transit commute, and at first could not handle both my long workday (which often includes standing) and standing on a bus, particularly when bumpy stretches on the bus ride hurt my abdomen. So, I took taxis to and from the office for my first six weeks back at work. And, lifting even pitchers of water caused painful twinges for several months after donation.
Be well, Snoopy