I dealt with what you are dealing with throughout HS. I never really found help for it, just pushed through it because it was during a sport season. Doing things like high knees or starting off a sprint was ridiculously painful.
I encountered this same problem in my training. I "strained" this area a couple different times - doing a 2rm on low box squats, doing a 1rm on squat, and doing a 1rm on sumo deadlifts. What did I do to fix this?
First I accepted the fact that doing max effort squat work weekly or even bi-weekly didn't agree with me. My hip strength and mobility in the hip was poor. I started doing standard straight sets/ramping sets on squats heavy one day (but never lower than 3-5 reps), and doing lighter dynamic work the other day.
But your question has nothing to do with squats - I just wanted to make sure what my situation was and what helped.
Using two resistance bands, one being a thicker black band and the other a "normal" green band, I would attach the larger band around my hip while lying down wedging it hard into the hip joint. With the green band attached behind me, I'd stretch it out and attach it around my heel/ankle area. These two bands pulling opposite angles seemed to "traction" my hip and my mobility was immediately better while reducing pain after a minute or so in the stretched position. Watch this video of Donnie Thompson demonstrating this (skip to 1:30) -
Using a short/thick resistance band similar to the Sling Shot Hip Circle (mine was an EliteFTS orange band), I would do sets of 10 side-steps and side lunges, until I felt warmed up. I'd also do a set of standing side kicks to further activate the glutes. After this, with the band still around my knees/lower thigh, I'd do a full squat while focusing on pushing my knees out. I'd even do this in my warm-ups from 45lbs to 135lbs.
These band stretches along with learning to train smarter helped my poor hip issues. I hope you find these things useful.