What to do about hip flexor tightness and pain?

Stretch/ICE. Recommend course of stretching, icing and anti-inflammories for 1-2 weeks. If not better, you may consider evaluation for other treatment options. Consider further imaging studies like x-ray or mri.
Work on stretching-- --Yoga is a great way 2 start. As far as the pain, once U limber up it should improve. Happens over months, B patient. .