Is a heavy feeling in your legs normal after starting a new walking routine?

I went for an hour and a half long walk two days ago, and a 40 minute walk yesterday, and my legs feel kind of heavy. Kind of like how they feel if I eat too much salt, but I don't think I ate anything really salty yesterday (I try to keep some idea of how much salt, sugar, crap, etc I eat each day). Also, my pants are slightly tighter on my calves and mid and lower thighs. Do my legs feel weird because of the walking, or something else? I am trying to tone up a bit and build some muscle =P