Hi! I think the injury I had around this time last year sounds very similar to yours.

It was a pain in my left thigh, just above the knee, and it would act up when I started a run, and then I could usually ignore it during the run, and then a few hours after it would get far worse (sometimes to the point that I couldn't bear weight on it). I saw many doctors who suggested it was muscle tightness from too much running, and that I should foam roll and rest.

The pain persisted for about 6 months, and I started to get another pain in my shin, which I figured was shin splints. I saw some doctors again, got x-rays, this also came back as nothing. Eventually I got a referral to a specialist, who sent me for bone scans and found that I had two stress fractures - one in my femur and one in my tibia.

Stress fractures often do not show up in x-rays, but they will show up in a bone scan or an MRI. I would suggest going for an MRI or (depending on where you live) a bone scan may be cheaper. I had to take two months off running and wear a walking cast for my tibia, but I'm FINALLY better and running again with no leg pain at all.

Not sure if your problem is the same, but there are a lot of similarities!