I've had hip problems since I was a child, and you can bet, whenever I get on my bike (which is every day, if I have my 'druthers) my hips are going to cramp. Hard. I stick a leg out and wiggle it while riding, and it usually helps.
Sometimes I have to wait for a stop and putting my legs down helps. Once in a while, I just have to deal with it until it goes away, shifting and wiggling all the time.
It's not the same issue you are experiencing, I'm just putting it out there to say that I understand your pain and need to ride, regardless.
Try some triple-strength glucosamine-chondrointin. It's a supplement, so is not federally regulated. Whatever the claims are cannot be proven. I've experienced positive results with it though, after a shoulder surgery I had. It really did help.
Take it as directed for about a month, and see if it helps. It did help my shoulder. You definitely want the triple-strength (it's a marketing gimmick, but that's the stuff you want).
A month's supply might cost you fifteen bucks at Walmart, and if it helps then WooHoo! If not... I've got nothing to offer that hasn't been said. Give it a try. Unless you're allergic to shellfish there's not much to lose.