Congratulations on your new hip!!! Glad to hear your doing so well at only 4 weeks. Be patient, healing takes a certain amount of time (especially the bones). Good nutrition, physical therapy and good rest will help but it still takes time.
I am 9 weeks post op and not a nutrition specialist. I have continued to take the same supplements and vitamins that I took previously. They include a multi-vitamin, fish oil, and glucoasmine with chrondroitin. I have added a calcium supplement and have been drinking more milk to help the bones grow. I also use whey protein powder to aid in muscle repair. Not sure if you should take an iron supplement but sounds like you may need to. You could also try to increase your iron intake with your diet. (red meat, dark leafy greens, beans, ect.)
I started riding a stationary bike during the second week and have done simple physical therapy streatching and excercises nearly every day. Since getting off crutches at 6 weeks I've been walking as much as possible and slowly increasing the distance and difficulty (hills). I also use a foam roller for deep tissue massage of the muscles effected by the operation.
Hope this helps, keep up the good work and positive attitude!