I'm unqualified to answer but will anyway. A one hour walk doesn't knock down most people that I know. You might be warn out or a little sore later if you're not used to it, but if that's really pushing your limit then I'd recommend looking into some things:

• Proper nutrition. I'm not saying "eat more lettuce". What I mean is getting plenty of protein and iron. Veggies too but with balance and regularity. Take a one a day vitamin, get a little B12 in there. Avoid junk food, make your meals count.
• Are you getting enough sleep? Nutrition and walking daily helps tremendously, this could fix itself.
• Get a blood panel from a doctor, see what your deficiencies are. Switch up your diet to help it unless a prescription is temporarily required.

If you can get used to moving and find joy in taking care of yourself, a one hour walk will fail to phase you after a while. If you're already taking care of yourself, getting professionally evaluated from a good doctor can help.