I feel your pain! Actually, I don't - I feel my own
. The same situation as you, but my dad lost the use of both hips. He spent the last 6 months of his life bed-ridden.
When you've seen what bad hips can do, it is a big motivation to look after your own.
Obviously you need to make sure that your position on your bike is good and that you aren't using massive gears all the time.
Arthritis is perhaps the most likely culprit so get yourself down to the doctor so you know what you are dealing with.
I had x-rays a few years back and I was already showing signs of osteoarthritis. I've managed to minimise it's progression by lifestyle changes.
I've had to give up on running now because that hurts my hips too much.
I haven't been swimming for a while but if I go again, I won't be able to do a breaststroke kick.
Hill-walking is okay as long as I don't clamber over big boulders. I have to limit the range of motion of my legs and then I'm okay.
I'm okay on the bike as long as I use low gears (which I do) and am careful dismounting (I sometimes forget that and swing my leg too vigorously - it hurts!).
I take Glucosamine Sulphate and Cod Liver Oil supplements and I think that they help. There is quite a lot of scientific evidence to support their use. Plenty of articles on that subject if you Google for info.
Good luck!
PS Make sure you keep your weight down too. The heavier you are, the more wear and tear on your joints.