I think I'll write an answer out of my comment to be able to explain a bit further, because you didn't rule it out.
Maybe your legs are unevenly long, this is a pretty common problem. No ones legs are equally long, but for the most people the difference is too small to be noticed. I never noticed it for myself, neither did my father who is a physician, and I never had problems with it when I was young. Maybe it developed during puberty.
When I was 19 however during medical examination for medical service – serving was mandatory in Germany back then – the physician told me that my legs were differing in length, with the right leg about 1cm shorter. Up until to that moment I had never noticed this and I really didn't care about it afterwards.
Some, maybe three years ago, I started to feel pain in my pelvis and my the adductors in the right leg. It wasn't a really stinging pain but just annoying, so I ignored it for a long time. This year after I started being more active and feared that I could suffer long term damage and not be able to continue my sports, I finally decided to visit a Sports Medicine Doctor. He was not able to confirm the difference in my legs any more, because my pelvis has wrangled itself to even the shorter leg out. This causes higher stress on the tendons and especially the points where the muscles are connected to the bones, as these spots get twisted.
There is no good way I know of to diagnose it yourself as the pelvic might have adapted to the problem. I never really experienced the pain to worsen after any cardio activity (cycling, swimming, running), it was just there before and afterwards. But I think that one squatting session I did two weeks ago (without weights) however lead to increased pain.
If you can exclude all other factors, you might see a professional to have this condition checked. I have no idea who, other than a Sports MD is fit to diagnose this, Physiotherapists might be able, too.