i would reccomend having someone perform muscle tests on your hip flexors, adductors, abbuctors, and hamstrings too isolate if a particular group of muscles is weak...not just tight. tight and weak go hand in hand. weak muscles become tight. and yoga doesn't stregnthen those muscles.
that combined with a hip stabilization track (exercises much like those in pilates) should help.
but there could also be a biomechanical problem (the way your hip sockets/femoral head are positioned). it's hard to say...go spend some money and see someone if the problem lasts more than 2 weeks.