Alison,
I have personal experience in this area, and I can say you definitely want to see a specialist and get your hips X-rayed. If after several months the pain subsists, or gets worse, go see the specialist again and get a 2nd set of X-rays, the reason being it may be a progressive situation that might not be noticeable in the first set of X-rays. Having a specialist look at both sets of X-rays would enable them to see if there were any differences over time.
Not to "air my dirty laundry" in public, but I developed hip problems as a 14-year-old kid. I complained of pain that was intense but intermittent. I was X-rayed and the doctors didn't see anything unusual, and what I had wasn't diagnosed for about a year until I was X-rayed a 2nd time, and then had both sets examined by a specialist. Arguably, after viewing the first set of X-rays, I agree that the situation was barely noticeable and thus easily overlooked, but when looking at the 2nd set of X-rays taken a year later, the situation was obvious. In fact, I'd agree that it was only after viewing the 2nd set of X-rays that one could look back at the first set to notice the beginnings of a problem.
During that year's time between X-rays, the pain got worse and worse, and even simple walking became more and more strenuous and difficult. Check the pic below. The part labeled 'unstable' is like a knife edge, and it was cutting into my leg muscles as I walked. It was most pronounced immediately after either long periods of sitting, or after periods of physical exertion. Unfortunately, I developed it in both hips, but fortunately it was eventually diagnosed. The story I got from the doc who diagnosed it was that, left untreated, such a condition usually resulted in becoming permanently crippled. The treatment was an operation to put pins in both hips, and then to use a wheelchair for about 4 months and then crutches for about 6 weeks. After that, a bit of physical therapy, and before too long, I was back to normal with both hips retaining about 97% rotational range. Soon after that, I became very active; running, cycling, etc., thus a happy ending was possible in my case. Having been through all that, I can tell you that my mobility means everything to me.
Sorry to all if I've alarmed or upset or even bored anyone with this barrage of information, but I wouldn't wish what I had on anybody, so I'd want you to get it checked out by a professionlal ASAP. I hope this helps not only you, but also anyone else who has similar 'mysterious' problem that evades easy diagnosis.
Best of luck to you.