You will have trouble with those for a bit. They exercise areas that were stretched / distended during the surgery and need rejuvenation.
Both times, I had to relearn how to do the sideways leg raise in particular. It wasn't muscle strength (I thought), since my larger muscles were in shape, but I could not for the life of me even move the leg up. It was the most frustrating thing.
My PT worked with me, first raising it gently as I tried, eventually getting (yipee!!) one repetition. She told me that she also saw this in THR recoveries, that not only strength, but muscle memory has to be rebuilt.
After a couple of weeks, I began to be an old pro and did five reps with abandon and dash

You'll get there, sound like you're doing well. Have patience though - you will hit spots where you regress; we all have. Just work past them, trust your body and keep within the restrictions that your surgeon has put up for you.