There are many possible reasons for the difference. You didn't mention how long it's been since your surgery compared to your sisters' operations. Many patients expect results too soon. Total hip replacement is a major operation. It takes weeks to months for bone to grow around the implant and help seal it in place. Some of the hip muscles are cut during the operation and must knit back together, too.
The type of implant and method used to put it in place can vary too. Both of these factors can make a difference. Rehab and a home exercise program must be followed carefully for a good result.
Tell your doctor about your concerns at your next follow-up visit. It may just be too early to know what your final outcome will be.