Athlete knee pain

16M I do MMA (mixed martial arts) and I've been doing it for around 4 years and have had zero injuries or pain besides muscle pain from time to time but ever since the beginning of this year I've had a funky knee. When I went down on my knees to grapple (Jiu Jitsu) I felt a funny pain underneath my kneecap but i ignored it. Fast forward a few months it hasn't gone away and sort of fades in and out. Sometimes it pains (only when I'm sitting on my knees) sometimes it doesn't pain. But recently my knee has had a popping sensation when I do certain moves. One of these moved are called "the triangle choke" and basically your knee is sideways and is pressed against your chest. When I do this move and I release from the move and straighten my leg it kind of pops into place? Its not pleasant but it's not painful either. After my training session there's no swelling but my knee often gets hot. Currently my issue is that funny popping and the fact my knee pains when it's bent such as sitting down on a chair or sitting on my knees. What should i and what is this?