I ruptured my achilles tendon and 3 weeks post op. When I get up on crutches blood rushes to my foot. Normal?

When I do get up the blood rushes to my foot, my toes turn dark from the blood and my foot swells a little. Makes it very uncomfortable and keeps me from getting out. I have been keeping my foot elevated at all times and ice off and on thoughout the day. Is this normal? When can I expect this to stop?