Myelodysplastic Syndromes (MDS) and leg weakness.

Over the last few months it seems like if I walk maybe 1000 ft my legs feel weak, and I feel like crap. If I set down and take it easy in my easy chair for 30 -45 mins I feel about the same as before the walk. My white and red and platelets are low, but I assume the weakness is caused by low red cells. You thoughts please.